ANSI/NISO Z39.50-1992 ISSN: 1041-5653 (Revision of ANSI/NISO Z39.50-1988)
This is one of a set of standards produced to facilitate the interconnection of computer systems. It is positioned with respect to other related standards by the Open Systems Interconnection (OSI) basic reference model (ISO 7498). The aim of Open Systems Interconnection is to allow the interconnection of computer systems with a minimum of technical agreement outside the interconnection standards.
This standard defines a protocol within the application layer of the reference model, and is concerned in particular with the retrieval of information stored in machine readable databases.
1.1 Scope and Field of Application
This standard describes the Information Retrieval application service (section 3) and specifies the Information Retrieval application protocol (section 4), for Open Systems Interconnection.
The Information Retrieval application service is described in terms of services that provide capabilities within an application. The description neither specifies nor constrains the implementation within a computer system. The purpose of the service description is to define the functions that the protocol must support.
The protocol specification includes the definition of the protocol control information, the rules for exchanging this information, and the conformance requirements to be met by implementation of this protocol.
This standard is intended particularly for use by systems supporting information retrieval services for organizations such as libraries, information utilities, and union catalogue centers. It addresses connection-oriented, program-to-program communication utilizing telecommunications. It does not address the interchange of information with terminals or via other physical media.
1.2 Model
The objective of this standard is to facilitate the open interconnection of database users with database providers. It is necessary to distinguish between the set of OSI standards and the hardware and software implementation of a system using the protocols specified in these standards. The ways in which databases are implemented differ considerably; different systems have different styles for describing the storage of data and the means by which it can be accessed. A common, abstract model is therefore used in describing databases, to which an individual system can map its implementation. This enables different systems to communicate in standard, mutually understandable terms.
The term "database" as used in this standard refers to a collection of one or more files, each with a unique name. A group of files within a database may also have a name and be accessed as a single database. The unit of information for retrieval from a database is a record. All of the records within a given file have a common structure, contain a common set of data elements and a common set of access points. An access point is a unique or non-unique key which can be specified either singly or in combination with other access points in a search for records. An access point may be equivalent to a data element, may be derived from a data element, or may be the combination of all or part of two or more data elements.
A search query may be applied to a database, specifying values to be matched against the access points of the database. The subset of records formed by applying the search query is termed the result set. A result set may itself be referenced in a subsequent search query statement and be manipulated to form a new result set.
For generality, it is assumed that query processing does not necessarily require physical access to records; a result set is thus assumed to be the identification of (e.g. pointers to) records, as opposed to the actual set of records, selected by a query. (It is not assumed that the database records are locked. Methods of concurrency control, which would prevent modification or deletion of result set records, are not addressed by this standard.) A result set may be used as a selection mechanism for the transfer of records between systems; the result set itself is considered to be a purely local data structure and is not transferred (that is, records are transferred, but not the local pointers to the records).
A generic search query statement is composed of a database name followed by a query statement. The Type-1 query statement defined in this standard consists of either a single access point clause, or several access point clauses linked by logical operators. For example:
1.3 References
ANSI/NISO Z39.58-1992--Common Command Language for Online Interactive Information Retrieval. ISO 2709--Documentation - Format for Bibliographic Information Interchange on Magnetic Tape 1981. ISO 4217--Codes for the representation of currencies and funds 1990. ISO 7498--Information Processing Systems - Open Systems Interconnection - Basic Reference Model 1984. ISO TR 8509--Information Processing Systems - Open Systems Interconnection - Service Conventions 1987. ISO 8649--Information Processing Systems - Open Systems Interconnection - Service Definition for the Association Control Service Element 1987. ISO 8650--Information Processing Systems - Open Systems Interconnection - Protocol Specification for the Association Control Service Element 1987. ISO 8777--Information and Documentation - Commands for Interactive Text Searching. ISO 8822--Information Processing Systems - Open Systems Interconnection - Connection Oriented Presentation Service Definition 1988. ISO 8824--Information Processing Systems - Open Systems Interconnection - Specification of Abstract Syntax Notation One (ASN.1) 1987. ISO 8825--Information Processing Systems - Open Systems Interconnection - Specification of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1) 1987. ISO 9545--Information Processing Systems - Open Systems Interconnection - Application Layer Structure 1989. ISO 10163--Information and Documentation - Search and Retrieve Application Protocol Specification for Open Systems Interconnection 1991.