193. Model Level InterfaceWe now describe the Cedar interface to the implementation of the Cypress data model. We assumethat the reader is familiar with the basic conceptual data model, i.e., has read the previous section.Our presentation is therefore slightly different in this section: we describe the procedures in thedatabase interface in roughly the order that a client will want to use them in a program. We presenttypes and initialization, schema definition, the basic operations, and then queries. It should be emphasized that the interface we are about to describe is only one possibleimplementation of the abstract data model described in Section 2. For example, we have chosen toimplement a procedural interface called by Cedar programs, and to do type checking at run-time.3.1 TypesIn this subsection we describe the most important types in the interface. Less pervasive types aretreated at the point where they are first used.Entity: TYPE;Relship: TYPE;An Entity or Relship is not the actual database entity or relationship; they are handles for the actualdatabase objects. All accesses to database objects are performed by calling interface procedures withthe handles as parameters. Even comparisons of two entities for equality must be done in this way.The Entity and Relship handles are allocated from storage and automatically freed by the garbagecollector when no longer needed.Value: TYPE = REF ANY;ValueType: TYPE;Datatype: TYPE;StringType, IntType, BoolType, AnyDomainType: DataType;Storing Cedar data values in tuples presents several problems. First, since we would like to define asingle operation to store a new value into a specified attribute of a Relship (for instance), there mustbe a single type for all values that pass through this "store-value" procedure. This is the type Valueabove, represented as untyped REFs in Cedar. The DataTypes will be discussed in the next section.Entities, strings, integers, and booleans are the types of values the system currently recognizes andallows as attribute values. More precisely, these four types are Entity, ROPE, REF INT, and REFBOOL. In the case of an entity-valued attribute, an attribute's type may be AnyDomainType or aspecific domain may be specified. The latter is highly preferred, as AnyDomainType is a loopholein the type mechanism and limits the kinds of operations that can be performed automatically by theGfp ^q Zp&9 XF V8, TVF R"U NF  < L># I*5 Cr ?pY =v/ 9sX 7f 3pspsp:tp 1UT /!30 ,spsp'# * &sX $ "s ?7 cpL /Fsp ^s pspsp' a ]Bspspsps )p@s p Fs p c h y?Q]CYPRESS DOCUMENTATION20database system or associated tools. We currently provide no mechanism to store compound Cedardata structures such as arrays, lists, or records in a database; the database system's data structuringmechanisms should be used instead. Cypress query operations such as RelationSubset cannot becomposed upon data that appears as uninterpreted bits in the database.Note that a Value may be either an Entity or a Datum. Some operations accept any Value, e.g.SetF; others require an Entity, e.g. NameOf. Others may require an Entity from a particular client-defined domain, e.g. a Person. We might think of the hierarchy of built-in and client defined typesand instances of values like this:Value type hierarchyDatabase representative of typeValue (REF ANY)ValueType Datum DatumType ROPE StringType INT IntType BOOL BoolType Entity AnyDomainType person Entity Person domain employee Entity Employee domain ... other client-defined entities ... ... other client-defined domains ...As Cedar doesn't have a good mechanism for defining type hierarchies or new types for client-defined domains, most Cypress operations simply take a REF ANY or an Entity as argument,performing further type checking at run-time.3.2 Transactions and segmentsIn this section we describe the basic operations to start up a database application's interaction withCypress. The client application's data is stored in one or more segments, accessed undertransactions. The Cypress system currently runs on the same machine as the client program,however transactions are implemented by the underlying file system which may reside on anothermachine. Data in remote segments may therefore be concurrently accessed by other instances ofCypress on other client machines.A transaction is a sequence of read and write commands. The system supports the property that theentire sequence of commands executes atomically with respect to all other data retrieval and updates,that is, the transaction executes as if no other transactions were in progress at the same time.Because there may in fact be other transactions accessing the same data at the same time, it ispossible that two transactions may deadlock, in which case one of them must be aborted. So the"fpuFpu Mp _%: \M ZZ XxF T spspspsp Rhspspspsp P4sp6 M"H% YH|r%H%H|r+`H%H|FHs%D% A% ?% =v% ;A%9 p s%psp6s%psp4)%( 0A .(spsp ,_- &r #pf  S  I cF /K ! D %t p1 *6 F MF M ?Q]<MODEL LEVEL INTERFACE21price paid for concurrent access is that programs be prepared to retry aborted transactions.The database system provides the capability of accessing a database stored on the same machine asthe database client, using the Pilot file system or on Alpine file servers. We currently permit onlyone transaction per segment per instance of the database software on a client machine. That is, datain remote segments may concurrently be updated by application programs under separatetransactions, but on the same machine transactions are used simply to make application transactionson their respective segments independent. This transaction-per-segment scheme is a majorsimplification of the Cypress package. In addition, as we shall see presently, nearly all Cypressprocedures can automatically infer the appropriate segment and transaction from the procedurearguments, avoiding the need to pass the transaction or segment for every database operation. Calls to Initialize, DeclareSegment, and OpenTransaction start the database session. Atransaction is either passed in by the client, or created by the database package (the latter is just aconvenience feature). The operation MarkTransaction below forms the end of a databasetransaction and the start of a new one. The operation AbortTransaction may be used to abort atransaction. Data in a database segment may not be read or updated until the segment andtransaction have been opened. Clients must decide when to tell the system that a transaction iscomplete (with CloseTransaction), and must be prepared to deal with unsolicited notification thatthe current transaction has been aborted because of system failure or lock conflict.The client's interaction with the database system begins with a call to Initialize:Initialize: PROC[ nCachePages: CARDINAL_ 256, nFreeTuples: CARDINAL_ 32, cacheFileName: ROPE_ NIL ];Initialize initializes the database system and sets various system parameters: nCachePages tells thesystem how many pages of database to keep in virtual memory on the client's machine,nFreeTuples specifies the size to use for the internal free list of Entity and Relship handles, andcacheFileName is the name of the disk file used for the cache backing store. Any or all of thesemay be omitted in the call; they will be given default values. Initialize should be called before anyother operation; the schema declaration operations generate the error DatabaseNotInitialized if thisis violated.Before database operations may be invoked, the client must open the segment(s) in which the dataare stored. The location of the segment is specified by using the full path name of the file, e.g."[MachineName]SubDirectory>SegmentName.segment". Each segment has a uniquename, the name of a Cedar ATOM which is used to refer to it in Cypress operation. The name ofthe Cedar ATOM is normally, though not necessarily, the same as that of the file in which it is"SfpuFpupuGp _\ [:^ Y$A VF T'L( RhJ P4Q MD KS I? E!spsp" C` AR  sp" ?7sp <3& :?! 8sp 4 6KT 2pHs .X ,_ *+ ' $ p&s p ! J s p#spsp }s pK I.s p Fsp  N 8+ O gsp4 3 sp%, >Q^(CYPRESS DOCUMENTATION22stored, except the extension ".segment" and the prefix specifying the location of the file is omitted inthe ATOM. If the file is on the local file system, its name is preceded by "[Local]". For example,"[Local]Foo" refers to a segment file on the local disk named Foo.database;"[Alpine]Baz" refers to a segment named Baz.segment on the directory onthe Alpine server. It is generally a bad idea to access database segments other than through thedatabase interface. However, because segments are physically independent and contain no referencesto other files by file identifier or explicit addresses within files, the segment files may be movedfrom machine to machine or renamed without effect on their contents. If a segment file in a set ofsegments comprising a client database is deleted, the others may still be opened to produce adatabase missing only that segment's entities and relationships. A segment is defined by theoperation DeclareSegment:DeclareSegment: PROC[ filePath: ROPE, segment: Segment, number: INT_ 0, readOnly: BOOL_ FALSE, version: Version_ OldOnly, nBytesInitial, nBytesPerExtent: LONG CARDINAL_ 32768] RETURNS [Segment];Segment: TYPE = ATOM;Version: TYPE = {NewOnly, OldOnly, NewOrOld};The version parameter to DeclareSegment defaults to OldOnly to open an existing file. The signalIllegalFileName is generated if the directory or machine name is missing from fileName, andFileNotFound is generated at the time a transaction is opened on the segment if the file does notexist. If version NewOnly is passed, a new segment file will be created, erasing any existing one. Inthis case, a number assigned to the segment by the database administrator must also be passed. Thisnumber hack is necessitated by our current implementation of segments (it specifies the section of the database addressspace in which to map this segment). Please bear with us. Finally, the client program can passversion=NewOrOld to open a new or existing segment file; in this case the segment number mustalso be passed, of course.The other parameters to DeclareSegment specify properties of the segment. If readOnly=TRUE,then writes are not permitted on the segment; any attempt to invoke a procedure which modifiesdata will generate the error ProtectionViolation. nBytesInitial is the initial size to assign to thesegment, and nBytesPerExtent is the incremental increase in segment size used when more space isrequired for data in the file.For convenience, a call is available to return the list of segments that have been declared in thecurrent Cypress session: "fpuFpu Mp _+= \sp N Z7 XxZ VDK TM Q V O*9 Mr<! K>] I  s p E-sX B3 @3 >7 <\ 8 6K- 2ppsp s p sp 0;sp.sp .s p1$ +spM ) sp6u '"U %|p& #Gsp9 ! 7s p s p 9% sps p  spA e .4 U > M?QYMODEL LEVEL INTERFACE23GetSegments: PROC RETURNS[LIST OF Segment ];A transaction is associated with a segment by using OpenTransaction: OpenTransaction: PROC[ segment: Segment, userName, password: ROPE_ NIL, useTrans: Transaction_ NIL ];If useTrans is NIL then OpenTransaction establishes a new connection and transaction with thecorresponding (local or remote) file system. Otherwise it uses the supplied transaction. The sametransaction may be associated with more than one segment by calling OpenTransaction with thesame useTrans argument for each. The given user name and password, or by default the logged inuser, will be used if a new connection must be established.Any database operations upon data in a segment before a transaction is opened or after a transactionabort will invoke the Aborted signal. The client should catch this signal on a transaction abort,block any further database operations and wait for completion of any existing ones. Then the clientmay re-open the aborted transaction by calling OpenTransaction. When the remote transaction issuccessfully re-opened, the client's database operations may resume.Note that operations on data in segments under different transactions are independent. Normallythere will be one transaction (and one or more segments) per database application program. A clientmay find what transaction has been associated with a particular segment by callingTransactionOf: PROC [segment: Segment] RETURNS [Transaction];Transactions may be manipulated by the following procedures:MarkTransaction: PROC[trans: Transaction];AbortTransaction: PROC [trans: Transaction];CloseTransaction: PROC [trans: Transaction];MarkTransaction commits the current database transaction, and immediately starts a new one. Uservariables which reference database entities or relationships are still valid.AbortTransaction aborts the current database transaction. The effect on the data in segmentsassociated with the segment is as if the transactions had never been started, the state is as it was justafter the OpenTransaction call or the most recent MarkTransaction call. Any attempts to usevariables referencing data fetched under the transaction will invoke the NullifiedArgument error. A"SfpuFpupuGp _sX, [:p4sp W^sX U* R P Lpspwpsp J7, H|5sp FHspR D; @7X >spsp sp0 ;d 9/sp 7fD 3E 1U"B /!R +EsX= 'ip< #sX* , , pL M spM W spsp M,sp  >Q]CYPRESS DOCUMENTATION24call to OpenTransaction is necessary to do more database operations, and all user variablesreferencing database items created or retrieved under the corresponding transaction must be re-initialized (they may reference entities or relationships that no longer exist, and in any case they aremarked invalid by the database system).A simple client program using the database system might have the form, then:Initialize[];DeclareSegment["[Local]Test", $Test];OpenTransaction[$Test];...... database operations, including zero or more MarkTransaction calls ......CloseTransaction[TransactionOf[$Test]];3.3 Data schema definitionThe definition of the client's data schema is done through calls to procedures defined in this section.The data schema is represented in a database as entities and relationships, and although updates tothe schema must go through these procedures to check for illegal or inconsistent definitions, theschema can be read via the normal data operations described in the next section. Each domain,relation, etc., has an entity representative that is used in data operations which refer to that schemaitem. For example, we pass the domain entity when creating a new entity in the domain. The typesof schema items are:Domain, Relation, Attribute, Datatype, Index, IndexFactor: TYPE = Entity;Of course, since the schema items are entities, they must also belong to domains; there are pre-defined domains, which we call system domains, in the interface for each type of schema entity:DomainDomain, RelationDomain, AttributeDomain, DatatypeDomain, IndexDomain: Domain;There are also pre-defined system relations, which contain information about sub-domains, attributes,and indices. Since these are not required by the typical (application-specific) database client, wedefer the description of the system relations to Section 3.6. In general, any of the data schema may be extended or changed at any time; i.e., data operationsand data schema definition may be intermixed. However, there are a few specific orderingconstraints on schema definition we will note shortly. Also, the database system optimizes for betterperformance if the entire schema is defined before any data are entered. The interactive schema editing"fpuFpu Mp _spD \5* ZO Xx' TLPs N%LXJ#GpIEsC' =/r 9TpV 7,-tp 4] 2 tpL 0g .Mb , (=sXI $apE "-t p2 QsXS upY AG  =u 1pN P 60 Ju M L?Q\MODEL LEVEL INTERFACE25tool described in the database tools documentation allows the schema to be changed regardless of ordering constraints andexisting data, by recreating schema items and copying data invisibly to the user when necessary.All the data schema definition operations take a Version parameter which specifies whether theschema element is a new or existing one. The version defaults to allowing either (NewOrOld): i.e.,the existing entity is returned if it exists, otherwise it is created. This feature avoids separateapplication code for creating the database schema the first time the application program is run. DeclareDomain: PROC [name: ROPE, segment: Segment, version: Version_ NewOrOld, estRelations: INT_ 5] RETURNS [d: Domain];DeclareSubType: PROC[sub, super: Domain];DeclareDomain defines a domain with the given name in the given segment and returns itsrepresentative entity. If the domain already exists and version=NewOnly, the signal AlreadyExistsis generated. If the domain does not already exist and version=OldOnly, then NIL is returned.The parameter estRelations is used to estimate the largest number of relations in which entities ofthis domain are expected to participate.The client may define one domain to be a subtype of another by calling DeclareSubType. Thispermits entities of the subdomain to participate in any relations in which entities of thesuperdomains may participate. All client DeclareSubType calls should be done before declaringrelations on the superdomains (to allow some optimizations). The error MismatchedSegment isgenerated if the sub-domain and super-domain are not in the same segment.DeclareRelation: PROC [ name: ROPE, segment: Segment, version: Version_ NewOrOld] RETURNS [r: Relation];DeclareAttribute: PROC [ r: Relation, name: ROPE, type: ValueType_ NIL, uniqueness: Uniqueness _ None, length: INT_ 0, link: {Linked, Unlinked, Colocated, Remote}_ yes, version: Version_ NewOrOld] RETURNS[a: Attribute];Uniqueness: TYPE = {NonKey, Key, KeyPart, OptionalKey};DeclareRelation defines a new or existing relation with the given name in the given segment andreturns its representative entity. If the relation already exists and version=NewOnly, the signalAlreadyExists is generated. If the relation does not already exist and version=OldOnly, then NILis returned."SfpuFpupuGp _9u2G ](` YLp.sp& WM TQ RP NsX2 LH H) D psp sp Bup 0s @~p7spspsp >J s pI <( 89>s p 6J 3s p& 1up x sp /hI +sX )WR %| #G0 !1 O  7 p"sp sp W s p;spsps Up  & @QYCYPRESS DOCUMENTATION26DeclareAttribute is called once for each attribute of the relation, to define their names, types, anduniqueness. If version=NewOrOld and the attribute already exists, Cypress checks that the newtype, uniqueness, etc. match the existing attribute. The error MismatchedExistingAttribute isgenerated if there is a discrepancy. The attribute name need only be unique in the context of itsrelation, not over all attributes. Note this is the only exception to the data model's rule that names be unique in adomain. Also note that we could dispense with DeclareAttribute altogether by passing a list into the DeclareRelationoperation; we define a separate procedure for programming convenience.The attribute type should be a ValueType, i.e. it may be one of the pre-defined types (IntType,StringType, BoolType, AnyDomainType) or the entity representative for a domain. For pre-defined types, the actual values assigned to attributes of the relationship instances of the relationmust have the corresponding type: REF INT, ROPE, REF BOOL, or Entity. If the attribute has adomain as type, the attribute values in relationships must be entities of that domain or some sub-domain thereof. The type is permitted to be one of the pre-defined system domains such as theDomainDomain, thereby allowing client-defined extensions to the data schema (for example, acomment for each domain describing its purpose). The attribute uniqueness indicates whether the attribute is a key of the relation. If its uniquenessis NonKey, then the attribute is not a key of the relation. If its uniqueness is OptionalKey, then thesystem will ensure that no two relationships in r have the same value for this attribute (if a value hasbeen assigned). The error NonUniqueKeyValue is generated if a non-unique key value results froma call to the SetP, SetF, SetFS, or CreateRelship procedures we define later. Key acts the same asOptionalKey, except that in addition to requiring that no two relationships in r have the same valuefor the attribute, it requires that every entity in the domain referenced by this attribute must bereferenced by a relationship in the relation: the relationships in the relation and the entities in thedomain are in one-to-one correspondence. Finally, if an attribute's uniqueness is KeyPart, then thesystem will ensure that no two relationships in r have the same value for all key attributes of r,though two may have the same values for some subset of them.The length and link arguments to DeclareAttribute have no functional effect on the attribute, butare hints to the database system implementation. For StringType fields, length characters will beallocated for the string within the space allocated for a relationship in the database. There is noupper limit on the size of a string-valued attribute; if it is longer than length, it will be storedseparately from the relationship with no visible effect except for the performance of databaseapplications. The link field is used only for entity-valued fields; it suggests whether the databasesystem should link together relationships which reference an entity in this attribute. In addition, itcan suggest that the relationships referencing an entity in this attribute be physically co-located aswell as linked. Again, its logical effect is only upon performance, not upon the legal operations."fpuFpu Mp _spU \sp$ Z5 sp XxP VD$uN T3U R"F NFp sp sp&s L#p I>' G#xpxp EtE C@spE A s pM >1 : s p D 8sp3s p 60sp 4^sp 2) sps psp /s pDsp -L +26 )W(+sp '# %sptpsp $< !spsp sp0 6s psp X u =sp AK  sp9 U R oM : M(>QXPMODEL LEVEL INTERFACE27DestroyRelation: PROC[r: Relation];DestroyDomain: PROC[d: Domain];DestroySubType: PROC[sub, super: Domain];Relations, domains, and subdomain relationships may be destroyed by calls to the above procedures.Destroying a relation destroys all of it relationships. Destroying a domain destroys all of its entitiesand also any relationships which reference those entities. Destroying a sub-domain relationship hasno effect on existing domains or their entities; it simply makes entities of domain sub no longereligible to participate in the relations in which entities of domain super can participate. Existingrelationships violating the new type structure are allowed to remain. Existing relations and domains may only bemodified by destroying them with the procedures above, with one exception: the operationChangeName (described in Section 3.4) may be used to change the name of a relation or domain.DeclareIndex: PROC [ relation: Relation, indexedAttributes: AttributeList, version: Version];DeclareIndex has no logical effect on the database; it is a performance hint, telling the databasesystem to create a B-Tree index on the given relation for the given indexedAttributes. The indexwill be used to process queries more efficiently. Each index key consists of the concatenated valuesof the indexedAttributes in the relationship the index key references. For entity-valued attributes,the value used in the key is the string name of the entity. The version parameter may be used as inother schema definition procedures, to indicate a new or existing index. If any of the attributes arenot attributes of the given relation then the signal IllegalIndex is generated.The optimal use of indices, links, and colocation, as defined by DeclareIndex and DeclareAttribute,is complex. It may be necessary to do some space and time analysis of a database application tochoose the best trade-off, and a better trade-off may later be found as a result of unanticipatedaccess patterns. Note, however, that a database may be rebuilt with different links, colocation, orindices, and thanks to the data independence our interface provides, existing programs will continueto work without change.If a relation is expected to be very small (less than 100 relationships), then it might reasonably bedefined with neither links nor indices on its attributes. In the typical case of a larger relation, oneshould examine the typical access paths: links are most appropriate if relationships that pertain toparticular entities are involved, indices are more useful if sorting or range queries are desired.B-tree indices are always maintained for domains; that is, an index contains entries for all of theentities in a domain, keyed by their name, so that sorting or lookup by entity name is quick. Stringcomparisons are performed in the usual lexicographic fashion."SfpuFpupuGp _sX# [: W^) SpL QNE$ O X LTsp JEspu H|Ep) FHO Ds p1" @7sX >J :' p-) 7-spsp 5Q 3sp"+ 1UAsp /!H ,5s p )As psp &H $P "s04 ? X   /U :. U Y _ G M= > ?Q]CYPRESS DOCUMENTATION28DeclareProperty: PROC [ relationName: ROPE, of: Domain, type: ValueType, uniqueness: Uniqueness_ None, version: Version_ NewOrOld] RETURNS [property: Attribute];DeclareProperty provides a shorthand for definition of a binary relation between entities of thedomain "of" and values of the specified type. The definitions of type and uniqueness are the sameas for DeclareAttribute. A new relation relationName is created, and its attributes are given thenames "of" and "is". The "is" attribute is returned, so that it can be used to represent the propertyin GetP and SetP defined in the next section.3.4 Basic operations on entities and relationshipsIn this section, we describe the basic operations on entities and relationships; we defer the operationson domains and relations to the next section.A number of error conditions are common to all of the procedures in this section. Since values arerepresented as REF ANYs, all type checking must currently be done at run-time. The procedures inthis section indicate illegal arguments by generating the errors IllegalAttribute, IllegalDomain,IllegalRelation, IllegalValue, IllegalEntity, and IllegalRelship, according to the type of argumentexpected. The error NILArgument is generated if NIL is passed to any procedure that cannot acceptNIL for that argument. The error NullifiedArgument is generated if an entity or relationship ispassed in after it has been deleted or rendered invalid by transaction abort or close. DeclareEntity: PROC[ d: Domain, name: ROPE_ NIL, version: Version_ NewOrOld] RETURNS [e: Entity];DeclareEntity finds or creates an entity in domain d with the given name. The name may beomitted if desired, in which case an entity with a unique name is automatically created. If versionis OldOnly and an entity with the given name does not exist, NIL is returned. If version is NewOnlyand an entity with the given name already exists, the signal NonUniqueEntityName is generated.DeclareRelship: PROC [ r: Relation, avl: AttributeValueList_ NIL, version: Version_ NewOrOld] RETURNS [Relship];DeclareRelship finds or creates a relship in r with the given attribute values. If version isNewOnly, a new relship with the given attribute values is generated. If version is OldOnly, therelship in r with the given attribute values is returned if it exists, otherwise NIL is returned. If"fpuFpu Mp _sX \2 Z; Xx TpH Rhspsp5 P4sps p M X Kspsp Etr2 ApY ?d- ;12 9T s p6 75 s 4,ps p# 2 s psp. 0spsp* .MW *rsX (=9 &  "- p&sp As psp3sps p=sp sX H K o psp&sp ;sp3spsp  spEsp R M >Q]LMODEL LEVEL INTERFACE29version is NewOrOld, the relship with the given attribute values is returned if it exists, otherwiseone is created. If the creation of a new relship violates the key constraints specified byDeclareAttribute, the signal NonUniqueAttributeValue is generated.DestroyEntity: PROC[e: Entity];DestroyEntity removes e from its domain, destroys all relationships referencing it, and destroys theentity representative itself. Any client variables that reference the entity automatically take on thenull value (Null[e] returns TRUE), and cause error NullifiedArgument if passed to database systemprocedures. After an entity is destroyed, its old name may be re-used in creating a new one.DestroyRelship: PROC[t: Relship];DestroyRelship removes t from its relation, and destroys it. Any client variables that reference therelationship automatically take on the null value, and will cause error NullifiedArgument ifsubsequently passed to database system procedures.SetF: PROC[t: Relship, a: Attribute, v: Value];SetF assigns the value v to attribute a of relationship t. If the value is not of the same type as theattribute (or a subtype thereof if the attribute is entity-valued), then the errorMismatchedAttributeValueType is generated. If a is not an attribute of t's relation, IllegalAttributeis generated.GetF: PROC[t: Relship, a: Attribute] RETURNS [Value];GetF retrieves the value of attribute a of relationship t. If a is not an attribute of t's relation, errorIllegalAttribute is generated. The client should use the V2x routines described in the next section tocoerce the value into the expected type.SetFS: PROC [t: Relship, a: Attribute, v: ROPE];GetFS: PROC[t: Relship, a: Attribute] RETURNS [ROPE];GetFS and SetFS provide a convenient veneer on top of GetF and SetF that provide the illusionthat all relation attributes are string-valued. The effect is something like the Relational data model,and is useful for applications such as a relation displayer and editor that deal only with strings. Thesemantics of GetFS and SetFS depend upon the actual type of the value v of attribute a:"SfpuFpupuGp _spsp D \ K Zsp sp VsX R psp,! PF! N spspsp  LX*3 H|sX! D pspH Bl&!sp @72 <\sX/ 8psp spsp. 6KC 4spspsp s 1p .sX5 *+p spspspsp 'sp-* %( !sX0 5 pspspsp a mJ 9 spsp*sp sH >QS CYPRESS DOCUMENTATION30typeGetFS returnsSetFS assigns attribute to beStringTypethe string vthe string vIntTypev converted to decimal stringthe string converted to decimal integerBoolType"TRUE" or "FALSE"true if "TRUE", false if "FALSE"a domain Dthe name of the ref'd entitythe entity with name v(or null string if v is NIL)(or NIL if v is null string)AnyDomainTypesame, but includes domain:the entity with the given domain and name:(or NIL if v is null string)The same signals generated by GetF and SetF, such as IllegalAttribute, can also be generated bythese procedures. The string NIL represents the undefined value. The signal NotFound is generatedin the last case above if no entity with the given name is found.NameOf: PROC [e: Entity] RETURNS [s: ROPE];ChangeName: PROC [e: Entity, s: ROPE];NameOf and ChangeName retrieve or change the name of an entity, respectively. They generatethe signal IllegalEntity if e is not an entity.ChangeName should be used with caution. It is not quite equivalent to destroying and re-creating an entity with the newname but the same existing relationships referencing it. ChangeName is considerably faster than that, and furthermoreentity-valued variables which reference the entity are not nullified by ChangeName, though they would be byDestroyEntity. These features should be a help, not a hindrance. However, changing an entity name may invalidatereferences to the entity from outside the segment, e.g. in another segment or in some application-maintained file such as alog of updates. DomainOf: PROC[e: Entity] RETURNS [Domain];RelationOf: PROC[t: Relship] RETURNS [Relation];DomainOf and RelationOf can be used to find the entity representative of an entity's domain or arelationship's relation, respectively. The signal IllegalEntity is generated if e is not an entity. Thesignal IllegalRelship is generated if r is not a relationship.SegmentOf: PROC[e: Entity] RETURNS [Segment];SegmentOf returns the segment in which an entity is stored. It can be applied to domain, relation,or attribute entities.Eq: PROC [e1: Entity, e2: Entity] RETURNS [BOOL];Eq returns TRUE iff the same database entity is referenced by e1 and e2. This is not equivalent tothe Cedar expression "e1 = e2", which computes Cedar REF equality. If e1 and e2 are in"fpuFpu Mp ^._v`^ _X -^_ \s ` - Z`-' Xx`- VD `-`T- Q `-)`O- Kpspsp sp  Isp-sp GbA CsX+ AR& =vps p( ;A s psp 7ut 5G/ 37yu+ 1B0 /2I - *+sX+ '0 $ps p. !3s p) spsp sX- pE  sX1 ;psp/spsptp sp*spsp  M >Q]L+MODEL LEVEL INTERFACE31different segments, Eq returns true iff they have the same name and their domains have the samename.Null: PROC [x: EntityOrRelship] RETURNS [BOOL];Null returns TRUE iff its argument has been destroyed, is NIL, or has been invalidated by abortionof the transaction under which it was created.GetP: PROC [e: Entity, aIs: Attribute, aOf: Attribute_ NIL] RETURNS [Value];SetP: PROC [e: Entity, aIs: Attribute, v: Value, aOf: Attribute_ NIL] RETURNS[Relship];GetP and SetP are convenience routines for a common use of relationships, to represent"properties" of entities. Properties allow the client to think of values stored in relationshipsreferencing an entity as if they are directly accessible fields (or "properties") of the entity itself. Seethe figure on page 15 illustrating properties. GetP finds a relationship whose from attribute is equal to e,and returns that relationship's to attribute. The from attribute may be defaulted if the relation isbinary, it is assumed to be the other attribute of to's relation. If it is not binary, the current implementationwill find the "first" other attribute, where "first" is defined by the order of the original calls calls to DeclareAttribute.SetP defaults the from attribute similarly to GetP, but operates differently depending on whetherfrom is a key of the relation. Whether it is a key or not, any previous relationship that referenced ein the from attribute is automatically deleted. In either case, a new relationship is created whosefrom attribute is e and whose to attribute is v. SetP returns the relationship it creates for theconvenience of the client. GetP and SetP can generate the same errors as SetF and GetF, e.g. if eis not an entity or to is not an attribute. In addition, GetP and SetP can generate the errorIllegalProperty if to and from are from different relations. GetP generates the errorMismatchedPropertyCardinality if more than one relationship references e in the from attribute; ifno such relationships exist, it returns a null value of the type of the to attribute. SetP allows anynumber of existing relationships referencing e; it simply adds another one (when from is a key, ofcourse, there will always be one relationship). GetPList: PROC [e: Entity, to: Attribute, from: Attribute_ NIL] RETURNS [LIST OF Value];SetPList: PROC [e: Entity, to: Attribute, vl: LIST OF Value, from: Attribute_ NIL];GetPList and SetPList are similar to GetP and SetP, but they assume that any number ofrelationships may reference the entity e with their from attribute. They generate the signalMismatchedPropertyCardinality if this is not true, i.e. the from attribute is a key. GetPList returnsthe list of values of the to attributes of the relationships that reference e with their from attribute.Cedar has LISP-like list manipulation facilities. SetPList destroys any existing relationships that reference ewith their from attribute, and creates Length[vl] new ones, whose from attributes reference e and"SfpuFpupuGp _sp3 \ YsX/ TVpsp)sp% R". NFsXL LW GbpspI E-%< BQu @pspsps >pspsp. <\3sp u/ :',Q 7sp spsp. 5spDs 3psp$5 1Usp sp sp spsp, /! spsp!spsp s ,psp$spsp *sp@spspspsp (sp*spsp &Otp,sp sp $-sp#sp !1  sXX S 'pspspsp$ 'sp sp% spspsp sp0sp sp Uu% psp3s p spsp spsp ?Q\2oCYPRESS DOCUMENTATION32whose to attributes are the elements of vl. GetPList and SetPList may generate any of the errorsthat GetF and SetF may generate, and the error IllegalProperty if to and from are from differentrelations.Note that the semantics of SetPList are not quite consistent with the semantics of SetP. SetPListreplaces the current values associated with a "property" with the new values (i.e., destroys and re-creates relationships); SetP adds a new property value, unless the aOf attribute is a key, in whichcase it replaces the current value. The semantics are defined in this way because this has proven themost convenient in our application programs.Examples of the use of the property procedures for data access can be found in Section 4.3.Properties are also useful for obtaining information about the data schema. For example, GetP[a,aRelationIs] will return the attribute a's relation, and GetPList[d, aTypeOf] will return all theattributes that can reference domain d.E2V: PROC[e: Entity] RETURNS[v: Value];B2V: PROC[b: BOOLEAN] RETURNS[v: Value];I2V: PROC[i: LONG INTEGER] RETURNS[v: Value];S2V: PROC[s: ROPE] RETURNS[v: Value];The x2V routines convert the various Cedar types to Values. The conversion is not normallyrequired for ropes and entities since the compiler will widen these into the REF ANY type Value.V2E: PROC[v: Value] RETURNS[Entity];V2B: PROC[v: Value] RETURNS[BOOLEAN];V2I: PROC [v: Value] RETURNS[LONG INTEGER];V2S: PROC [v: Value] RETURNS[ROPE];The V2x routines convert Values to the various Cedar types. The MismatchedValueType error israised if the value is of the wrong type. It is recommended that these routines be used rather thanuser-written NARROWs, as the representation of Values may change. Also, NARROWs of opaque typesdon't yet work in the Cedar compiler.3.5 Query operations on domains and relationsIn this section we describe queries upon domains and relations: operations that enumerate entitiesor relationships satisfying some constraint."fpuFpu Mp _spspspsp \spspspspspsp Z U sp0sps Stp#9 Qsptp"sp O`#C M,, H|K FH>s D pspsp A%sp ;sX' 9w( 7B- 5% 0_psp-sp! .*)7 *NsX$ (% %+ ## pspsp"sp );  wpsp uwu d%  r- ^p#@ *, M ?Q](MODEL LEVEL INTERFACE33RelationSubset: PROC[ r: Relation, constraint: AttributeValueList_ NIL] RETURNS [RelshipSet];NextRelship: PROC[rs: RelshipSet] RETURNS [Relship];PrevRelship: PROC[rs: RelshipSet] RETURNS [Relship];ReleaseRelshipSet: PROC [rs: RelshipSet];AttributeValueList: TYPE = LIST OF AttributeValue;AttributeValue: TYPE = RECORD [ attribute: Attribute, low: Value, high: Value_ NIL -- omitted where same as low or not applicable --];The basic query operation is RelationSubset. It returns a generator of all the relationships inrelation r which satisfy a constraint list of attribute values. The relationships are enumerated bycalling NextRelship repeatedly; it returns NIL when there are no more relationships. PrevRelshipmay similarly be called repeatedly to back the enumeration up, returning the previous relationship; itreturns NIL if the enumeration is at the beginning. ReleaseRelshipSet should be called when theclient is finished with the query.The constraint list may be NIL, in which case all of the relationships in r will be enumerated.Otherwise, relationships which satisfy the concatenation of constraints on attributes in the list will beenumerated. If an index exists on some subset of the attributes, the relationships will be enumeratedsorted on the concatenated values of those attributes. For a StringType, IntType, or TimeTypeattribute a of r, the contraint list may contain a record of the form [a, b, c] where the attributevalue must be greater or equal to b and less than or equal to c to satisfy the constraint. For anytype of attribute, the list may contain a record of the form [a, b] where the value of the attributemust exactly equal b. The Cedar ROPE literals "" and "\377" may be used in queries as aninfinitely large and infinitely small string, respectively. The signal MismatchedAttributeValueTypeis generated by RelationSubset if one of the low or high values in the list is of a different typethan its corresponding attribute.DomainSubset: PROC[ d: Domain, lowName, highName: ROPE_ NIL, searchSubDomains: BOOL_ TRUE, searchSegment: Segment_ NIL]"SfpuFpupuGp _sX \3 Z V4 R4 O) K>2 I  F D BlG =p s p5 ;spZ 9Ts psp(s 7pU 4sp*sp 2" .sp,sp +&C )51 'i$s psps %5p spsp'sp # spsp$ <sp! sp sp c8s /ps pspsp  ! sX    MD ?Q]CYPRESS DOCUMENTATION34 RETURNS [EntitySet];NextEntity: PROC[EntitySet] RETURNS [Entity];PrevEntity: PROC[EntitySet] RETURNS [Entity];ReleaseEntitySet: PROC[EntitySet];DomainSubset enumerates all the entities in a domain. If lowName and highName are NIL, theentire domain is enumerated, in no particular order. Otherwise, only those entities whose names arelexicographically greater than lowName and less than highName are enumerated, in lexicographicorder. If searchSubDomains is TRUE, subdomains of d are also enumerated. Each subdomain issorted separately. The searchSegment argument is currently only used if d is one of the systemdomains, e.g. the Domain domain. It is used to specify which segment to search.Analogously to relation enumeration, NextEntity and PrevEntity may be used to enumerate theentities returned by DomainSubset, and ReleaseEntitySet should be called upon completion.GetDomainRefAttributes: PROC [d: Domain] RETURNS [AttributeList];This procedure returns a list of all attributes, of any relation defined in d's segment, which referencedomain d or one of its superdomains. The list does not include AnyDomainType attributes, whichcan reference any domain. GetDomainRefAttributes is implemented via queries on the dataschema. GetDomainRefAttributes is useful for application-independent tools; most specificapplications can code-in the relevant attributes.GetEntityRefAttributes: PROC [e: Entity] RETURNS [AttributeList];This procedure returns a list of all attributes in which some existing relationship actually referencese, including AnyDomainType attributes.3.6 System domains and relationsIn this section we describe what one might call the schema schema, the pre-defined system domainsand relations which constitute the data schema for client-defined domains and relations. The typicaldatabase application writer may skip this section, since the schema declaration operations defined inSection 3.3 are adequate when the data schema is completely defined and known at the time aprogram is written. The system domains and relations we describe in this section are most useful forgeneral-purpose tools (e.g. for displaying, querying, or dumping any database), where the tools must"fpuFpu Mp _sX [:- W^- S" N pspspsp LH Jjspsp H6 spspu Fps p$sp  CP ? s ps p <s psp  9 sXA 4^p4sp 2)sp/s p /sp" -sp; +1 'sXA #p/8 sp s p s ur p4t p e'> 1)< G U Atp M L>Q\MODEL LEVEL INTERFACE35examine the data schema "on the fly".As noted earlier, the permanent repository for data describing user-defined data in a database is thedatabase's data schema, represented by schema entities and relationships. Schema entities aremembers of one of the pre-defined system domains: DomainDomain, RelationDomain,DatatypeDomain, and so on. Every client-defined domain, relation, or attribute contains arepresentative entity in these domains. Client-defined datatypes are not currently permitted, so theonly entities in the DataType domain are the pre-defined IntType, StringType, and BoolType.The information about the client-defined domains and attributes are encoded by relationships in thedatabase. Domains participate in the system relation dSubType, which encodes a domain typehierarchy:dSubType: Relation; dSubTypeOf: Attribute; -- the domain in this attribute is a super-type of dSubTypeIs: Attribute; -- the domain in this attributeThe dSubType has one element per direct domain-subdomain relationship, it does not contain thetransitive closure of that relation. However, it is guaranteed to contain no cycles. That is, thedatabase system checks that there is no set of domains d1, d2, ... dN, N>1, such that d1 is a subtypeof d2, d2 is a subtype of d3, and so on to dN, and d1=dN. The dSubType may define a lattice asopposed to a tree, i.e. the sSubType attribute is not a key of the relation.The information about attributes is encoded as binary relations, one relation for each argument tothe DeclareAttribute procedure defining properties of the attribute. The names are easy toremember; for each argument, e.g. Foo, we define the aFoo relation, with attributes aFooOf andaFooIs. The aFooIs attribute is the value of that argument, and the aFooOf attribute is [the entityrepresentative of] the attribute it pertains to. Thus we have the following relations: aRelation: PUBLIC READONLY Relation; -- Specifies attribute - relation correspondence: -- [aRelationOf: KEY Attribute, aRelationIs: Relation] aRelationOf: PUBLIC READONLY Attribute; -- attribute whose relation we are specifying aRelationIs: PUBLIC READONLY Attribute; -- the relation of that attribute aType: PUBLIC READONLY Relation; -- Specifies types of relation attributes: -- [aTypeOf: KEY Attribute, aTypeIs: ValueType] aTypeOf: PUBLIC READONLY Attribute; -- the attribute aTypeIs: PUBLIC READONLY Attribute; -- domain or datatype of the attribute aUniqueness: PUBLIC READONLY Relation; -- Specifies attribute value uniqueness: -- [aUniquenessOf: KEY Attribute, aUniquenessIs: INT LOOPHOLE[Uniqueness]]"SfpuFpupuGp _% [:P Y-tp $ V?(tp s @ TpD Rhe P4 spsps psp LXN J#%sp G DsX AK ?8 ;pspF 912 7f$67f67f67f67f 51451451451451451451sp 2sp( /!+7 ,sp? *!spspsp (spsp2sp &OW "ssXX ?:  Y M mM 93 8 N gQ 3M J >Q^'CYPRESS DOCUMENTATION36 aUniquenessOf: PUBLIC READONLY Attribute; -- the attribute aUniquenessIs: PUBLIC READONLY Attribute; -- INT for Uniqueness: 0=None, 1=Key, etc. aLength: PUBLIC READONLY Relation; -- Specifies length of attributes: -- [aLengthOf: KEY Attribute, aLengthIs: INT] aLengthOf: PUBLIC READONLY Attribute; -- the attribute aLengthIs: PUBLIC READONLY Attribute; -- INT corresponding to attribute's length aLink: PUBLIC READONLY Relation; -- Specifies whether attribute is linked: -- [aLinkOf: KEY Attribute, aLinkIs: INT] aLinkOf: PUBLIC READONLY Attribute; -- the attribute aLinkIs: PUBLIC READONLY Attribute; -- 0=unlinked, 1=linked, 2 =colocated The final set of system relations pertain to index factors. Each index on a relation is defined toinclude one or more attributes of a relation. For each attribute in the index, there is an index factorentity. For each index, there is an index entity. Each index factor is associated with exactly oneindex and exactly one attribute. Indices may have many index factors, however, and an attributemay be associated with more than one index factor, since attributes may participate in multipleindices. The two relations pertaining to indices map indices on to their index factors, and indexfactors to the attributes they index: ifIndex: PUBLIC READONLY Relation; -- Specifies the index factors for each index -- [ifIndexOf: KEY IndexFactor, ifIndexIs: Index] ifIndexOf: PUBLIC READONLY Attribute; -- the index factor ifIndexIs: PUBLIC READONLY Attribute; -- index of the factor ifAttribute: PUBLIC READONLY Relation; -- Specifies attribute index factor corresponds to -- [ifAttributeOf: KEY IndexFactor, ifAttributeIs: Attribute] ifAttributeOf: PUBLIC READONLY Attribute; -- the index factor ifAttributeIs: PUBLIC READONLY Attribute; -- the attribute this factor representsThe relations on attributes, index factors, and domains can be queried with the RelationSubset orGetPList operations. For example, GetP[a, aRelationIs] returns the attribute a's relation.GetPList[r, aRelationOf] returns the relation r's attributes. RelationSubset[dSubType,LIST[[dSubTypeIs, d]]] will enumerate all the dSubType relationships in which d is the subtype.As noted earlier, the data schema (attributes, relations, domains, indices, index factors, and relationspertaining to these) may only be read, not written by the database client. In order to ensure theconsistency of the schema, it must be written indirectly through the schema definition procedures:DeclareDomain, DeclareRelation, DeclareAttribute, and DeclareSubType. Attempts to perform"fpuFpu Mp _sX> \X XxG VD1 T: QU MrL K>- I 8 FO Bp-t p& @#E >d <\@ :'V 75- 5% 1sXR /5 -z> +EA &[ $A "sA ?U cp;s p /spsp  sp ssptsps pspsp 9/ E H Mspsps p  Z M ?Q]MODEL LEVEL INTERFACE37updates through operations such as SetP result in the error ImplicitSchemaUpdate.3.7 ErrorsWhen a database system operation invokes an error, the SIGNAL Error is generated, with an errorcode indicating the type of error that occured. The error code is a Cedar enumerated type:Error: SIGNAL [code: ErrorCode];ErrorCode: TYPE = {AlreadyExists, -- Entity already exists and client said version=NewOnlyBadUserPassword, -- On an OpenTransactionDatabaseNotInitialized, -- Attempt to do operation without calling InitializeFileNotFound, -- No existing segment found with given nameIllegalAttribute, -- Attribute not of the given relship's Relation or not an attributeIllegalValueType, -- Type passed DeclareAttribute is not datatype or domainIllegalDomain, -- Argument is not actually a domainIllegalFileName, -- No directory or machine given for segmentIllegalEntity, -- Argument to GetP, or etc., is not an EntityIllegalRelship, -- Argument to GetF, or etc., is not a RelshipIllegalRelation, -- Argument is not a relationIllegalSegment, -- Segment passed to DeclareDomain, or etc., not yet declaredIllegalString, -- Nulls not allowed in ROPEs passed to the database systemIllegalSuperType, -- Can't define subtype of domain that already has entitiesIllegalValue, -- Value is not REF INT, ROPE, REF BOOL, or EntityIllegalValueType, -- Type passed DeclareAttribute is not datatype or domainImplicitSchemaUpdate, -- Attempt to modify schema with SetP, DeclareEntity, etc.InternalError, -- Impossible internal state (possibly bug or bad database)MismatchedProperty, -- aOf and aIs attribute not from the same relationMismatchedAttributeValueType, -- Value not same type as required (SetF)MismatchedExistingAttribute, -- Existing attribute is different (DeclareAttribute)MismatchedExistingSegment, -- Existing segment is different (DeclareSegment)MismatchedPropertyCardinality, -- Did GetP with aOf that is not a KeyMismatchedSegment, -- Attempt to create ref across segment boundary (SetF)MismatchedValueType, -- value passed V2E, V2I, etc. not of expected typeMultipleMatch, -- More than one relationship satisfied avl on DeclareRelship.NonUniqueEntityName, -- Entity in domain with that name already existsNonUniqueKeyValue, -- Relship already exists with that valueNotFound, -- Version is OldOnly but no such Entity, Relation, or etc foundNotImplemented, -- Action requested is not yet implementedNILArgument, -- Attempt to perform operation on NIL argumentNullifiedArgument, -- Entity or relationship has been deleted or invalidatedProtectionViolation, -- Read or write to segment not permitted this user.SegmentNotDeclared, -- Attempt to open transaction w/o DeclareSegmentServerNotFound -- File server does not exist or does not respond };"SfpuFpupuGp _#spsp Xr Tp7s p R0+ NsX LJjGH)FME :C@VAuK?3==<=:K>8.6M4J3 M1U@/K-P+J*+G(`G&R$L#E!6JkHMF <AJv:<LILE @  p>Q\CYPRESS DOCUMENTATION38In this report, the expression "generates the error X" means that the SIGNAL Error is generatedwith code=X. Unless otherwise specified, the client may CONTINUE from the signal, aborting theoperation in question. Signals should not be RESUMEd except by a wizard who knows the result ofproceeding with an illegal operation.Two special signals are associated with the file system level:Aborted: SIGNAL [trans: Transaction];Failure: SIGNAL [why: ATOM, server: ROPE];The Aborted signal can be generated by any database operation, and indicates that the transactionhas been aborted. The client must call AbortTransaction and may then call OpenTransaction toproceed. The Failure signal is generated when a transaction cannot be open due to server failure orcommunication difficulties."fpuFpu Mp _3s p \)sp Zsp+ Xx% T>PsX%N* Jpsp3# H'spsp F spO DZ$ MD>Q#j TIMESROMAN  TIMESROMAN  TIMESROMAN  HELVETICA  TIMESROMAN  TIMESROMAN HELVETICA  HELVETICAGACHA   TIMESROMAN #!)/ 8@GNU]ciow~/j/P>CypressDoc3.bravoCattellJune 15, 1983 9:45 AM