[Table of Contents | Previous Section | Next Section]

2. Definitions

A-association -- See Application association.

Abstract database record--An abstract representation of the information in a database record. An abstract database record may be formed by the application of an abstract record structure (defined by a schema) to the database record. An element specification may be applied to an abstract database record forming another instance of the abstract database record.

Abstract record structure -- The primary component of a database schema. An abstract record structure applied to a database record results in an abstract database record.

Abstract syntax -- A description of a particular data type using an abstract syntax notation. It can be referenced by an OID (object identifier).

Abstract syntax notation -- A language that allows the denotation of data types in a representation-independent manner. ASN.1 is an example.

Access point -- A unique or non-unique key that can be specified either singly or in combination with other access points in a search for records. An access point may be equivalent to an element (defined by an abstract syntax), derived from a set of one or more elements, or unrelated to any element.

Access point clause -- An operand of a type-1 query (informal).

Aggregate present response -- Segment requests (if any) together with the Present response, for a Present operation.

APDU -- See Application Protocol Data Unit.

Application association -- A communication session between a database user and a database provider. It may consist of one or more consecutive Z-associations.

Application Protocol -- The rules governing the format and exchange of information between an origin and target.

Application Protocol Data Unit -- A unit of information, transferred between origin and target, whose format is specified by the Z39.50 protocol, consisting of application-protocol-information and possibly application-user-data.

Application Protocol Control Information --Information conveyed by an application protocol data unit.

AppliedVariant -- One of three usages for a variant specification. The applied variant is the variant specification that the target applied to an element included in a retrieval record. See also variantRequest and supportedVariant.

ARS -- See Abstract record structure.

ASN.1 -- Abstract Syntax Notation One, as specified in ISO 8824 and ISO 8825.

Attribute -- A characteristic of a search term, or one of several characteristic components which together form a characteristic of a search term.

Attribute element -- An attribute represented by a pair of components: an attribute type and a value of that type.

Attribute list -- A set of attribute elements and the attribute set id to which it belongs. An attribute list is combined with a search term to form an operand of a type-1 query. Usually, one of the attribute elements from the set corresponds to a normalized access point, against which the term (as qualified by the other attribute elements) is matched.

Attribute set -- A set of attribute types, and for each, a list of attribute values. Each type is represented by an integer, unique within that set (as identified by its attribute set id), and each value for a given type is unique within that type.

Attribute set id -- An OID that identifies an attribute set, to which an attribute element (within an attribute list) belongs.

Attribute type -- A component of an attribute element. An attribute set defines one or more attribute types and assigns an integer to each type (it also defines values specific to each type). For example, bib-1 assigns the integer 1 for the attribute type "Use."

Attribute value -- A component of an attribute element. An attribute set defines one or more values for each attribute type that it defines. For example, bib-1 defines the Use attribute "personal name."

Client -- The application that includes the origin; the database user.

Client system -- The system on which the client resides.

Composition specification -- A specification that may be included in a Present request to indicate the desired composition (elements and record syntax) of the retrieval records. It includes a schema identifier, element specification, and record syntax identifier.

Conditionally confirmed service -- A service that may be invoked as confirmed or non-confirmed. It is defined in terms of a request (from the origin or target) followed possibly by a response (from the peer). For example, Resource-control is a conditionally confirmed service, initiated by the target. See also Non-confirmed service and Confirmed service.

Confirmed service -- A service that is defined in terms of a request (from the origin or target) followed by a response (from the peer). For example, Search is a confirmed service, initiated by the origin; Access-control is a confirmed service initiated by the target. See also Non-confirmed service and Conditionally-confirmed service.

Database -- A collection of information units containing related information. Each unit is a database record.

Database record -- A local data structure representing an information unit in a database.

Database schema -- A common understanding shared by the origin and target of the information contained in the records of the database, which allows the subsequent selection of portions of that information via an element specification. A schema defines an abstract record structure, which, when applied to a database record, results in an abstract database record.

Data element -- See Element.

Element -- A unit of information defined by a schema.

ElementRequest -- A request, included with an element specification, for the retrieval of a specific element. The element request may include a variantRequest, indicating the desired variant form of the element.

Element set name -- An element specification in the form of a primitive name.

Element specification -- An instance of an element specification format, or an element set name. An element specification transforms an abstract database record into another instance of the abstract database record (this may be a null transformation). The element specification selects elements from the abstract database record, and possibly also specifies variant forms for those elements.

Element specification format -- A structure used to express an element specification.

Element specification identifier -- The object identifier of an element specification format, or an element set name.

Exceptional record size -- The maximum size of the record that may be included in a Present response, in the special case when a single, exceptionally large record (i.e. larger than preferred-message-size) is requested.

Facility -- A logical group of Z39.50 services; in some cases, a single service. For example, the Retrieval facility consists of the Present service and the Segment service; the Search facility consists of the Search service. Alternatively, a facility might not consist of services, but instead might use services of other facilities. For example, the Explain facility does not define any services, but uses the Search and Present services.

Final fragment -- A fragment that ends at the end of a record. See Fragment.

Fragment -- A proper substring of a record. (This definition is meaningful only in the context of level-2 segmentation, described in section 3.3.3; within that section, a record is considered to be a string of bytes.)

GRS -- Generic Record Syntax.

Initiating request -- A request that initiates an operation.

Intermediate fragment -- A fragment that neither starts at the beginning nor ends at the end of a record. See Fragment.

IR -- Information Retrieval.

Item -- (1) A result set item. (2) A bibliographic item; see ISO 10160.

Maximum segment size -- The largest allowable segment of an aggregate Present response (when segmentation is in effect).

Name -- A linguistic construct, expressed in some language, that corresponds to an object. A name denotes (i.e. identifies) the object to which it is bound.

Non-confirmed service -- A service that is defined in terms of a request from the origin or target, with no corresponding response. For example, Segment is a non-confirmed service initiated by the target. See also Confirmed service.

Object identifier -- An unambiguous, globally-recognized, registered identifier for a data object, assigned by a registration authority.

OID -- See Object identifier.

Operation -- An initiating request and the corresponding terminating response, along with intervening related messages. For example, a Search operation always includes a Search request and Search response, and may also include access control and resource control messages. Multiple concurrent operations may occur within a Z-association.

Operation type -- The name of an initiating request. For example a Search request initiates an operation whose type is "search."

Origin -- The entity that initiates a Z-association and initiates operations during the Z-association.

Origin service-user -- That portion of a client that makes requests upon the origin. See Service-user.

OSI -- Open Systems Interconnection.

P-context -- See Presentation context.

Preferred message size -- The maximum size of a Search response or Present response when no segmentation is in effect. It is expressed in terms of the sum of the sizes (in bytes) of the response records, not including protocol control information.

Presentation context -- The pairing of an abstract syntax with a transfer syntax, negotiated by the presentation layer, in order for that abstract syntax to be used during the application association.

Primitive -- See Service primitive.

Primitive Name -- A name whose internal structure is not required to be understood or have significance to users of the name.

Note: primitive name is not related to primitive.

Record syntax--An abstract syntax requested by the origin or used by the target to represent retrieval records. For a complete definition, see section 3.6.3.

Response record -- A retrieval record or a surrogate diagnostic record, representing a database record, in a Search response or (aggregate) Present response.

Result set -- A local data structure used as a selection mechanism for the transfer of records, identified by a query. Its logical structure is a named, ordered list of result set items, and possibly, unspecified information which may be used as a surrogate for the search that created the result set.

Result set item -- A database name, a pointer to a record within the database, and possibly, additional, unspecified information associated with the record.

Result set record -- An idiomatic expression referring to the database record represented by a result set item. See Result set.

Retrieval record -- The exportable structure defined by the application of a record syntax to an abstract database record.

RPN query -- A search query represented in reverse polish notation (RPN) format.

Schema -- See Database schema.

Segment -- A message that is sent (or is in preparation for transmission) by the target as part of an aggregate Present response, i.e. a Segment request or Present response.

Server -- The application that includes the target; the database provider.

Server system -- The system on which the server resides.

Service -- (1) A Z39.50 service, as in the "search" service; (2) an extended service, as in the "persistent result set extended service"; (3) the service-provider.

Service primitive -- An abstract, implementation-independent representation of an interaction between the service-user and the service-provider. The four types of service primitives are: Request, Indication, Response, and Confirmation.

Service-provider -- An abstraction of the totality of those entities (the origin and target) that provide a service to peer service-users. The concept of service-provider is employed to facilitate the specification of protocol procedures. It is used only within 4.2.2, to describe the protocol model.

Note: the service-provider is not related to the database provider nor to the provider of telecommunication services.

Service-user -- An origin service-user or a target service-user. That portion of a client or server that makes requests upon the origin or target respectively. The concept of service-user is employed to facilitate the specification of protocol procedures. It is used only within 4.2.2, to describe the protocol model.

Note: The service-user is not related to the database user.

Simple Present response -- An aggregate Present response consisting of a single segment, i.e., consisting of a Present response only, and no Segment requests.

Starting fragment -- A fragment that starts at the beginning of a record. See Fragment.

SupportedVariant -- One of three usages for a variant specification. A supportedVariant is a variant specification that the target lists as supported for a particular element. See also appliedVariant and variantRequest.

Surrogate diagnostic Record -- A diagnostic record supplied in place of a retrieval recor d, representing a database record.

Tag -- The identifier of an element (or of a node of the tagPath representing an element). It consists of a tagType and a tagValue.

TagPath -- A sequence of nodes from the root of a tree to the node that the tagPath represents (when the elements of a record are represented hierarchically, as a tree). Each node of a tagPath is represented by a tag. The end-node might be a leaf-node, in which case the tagPath represents an element; otherwise the tagPath represents the subtree whose root is that node.

TagSet -- The tagValues (and recommended data types) for a set of elements.

TagSetId -- an object identifier serving as a persistent identifier for a tagSet.

TagType -- A short-hand (integer) identifier for a tagSet. A schema definition may assign a tagType to a TagSetId, to identify a particular tagSet (within the context of the schema definition).

TagValue -- The identifier of an element (or of a node of the tagPath representing an element). It may be either integer or string, and it is qualified by a tagType.

Target -- The entity that accepts a Z-association.

Target service-user -- That portion of a server that makes requests upon the target. See Service-user.

Terminating response -- A response that ends an operation.

Transfer syntax -- A syntax that when paired with an abstract syntax forms a record syntax.

Triple -- A 3-tuple. (I.e. an n-tuple, where n = 3.)

Type-1 query -- See RPN Query.

Variant -- One of possibly several forms in which an element is available for retrieval. The origin may request, or the target present, an element according to a specific variant. The target may indicate what variants are available for an element.

Variant list -- A list provided by the target of the supportedVariants for a particular element.

VariantRequest -- One of three usages for a variant specification. A variantRequest is a variant specification occurring within an element request. See also appliedVariant and supportedVariant.

Variant set -- A definition of a set of classes; for each class, a set of types; and for each type, a set of values. A variant specification consists of a set of variantSpecifiers from a particular variant set.

Variant set identifier -- An OID identifying a variant set.

Variant Specification -- A variantRequest, appliedVariant, or supportedVariant. A variant specification is a sequence of triples, each of which is a variantSpecifier.

Variant Specifier -- A component of a variant specification. It consists of a class, a type defined for that class, and a value defined for that type.

Z-association -- See Z39.50-association.

Z39.50-association -- A session, explicitly established by the origin and either explicitly terminated by the origin or target, or implicitly terminated by termination of the A-association. Communication between origin and target is via a Z39.50-association within an application association. There may be multiple, consecutive Z-associations within an A-association.