Z39.50 This document provides terms, their definitions, and a list of acronyms to promote a common understanding of the Z39.50 information retrieval protocol. Use of the glossary can assist in understanding the principles/ concepts, operational models, functions/services, and purpose behind the Z39.50 standard. The compilers welcome additions, corrections, and refinements to the terms offered here. We will maintain and revise this document as appropriate. Abstract record structure: content and Provides a format for representing the organization of records in a database for interchange with other systems. This format is an abstract representation of the elements of information that are contained in a record. (See also Schema, Elements, and Tagsets.) Abstract record syntax: Allows the client and server to agree upon common semantics and data layout of retrieved records. It is used as a mechanism to package a database record for transmission from server to client. Z39.50 specifies the use of a number of record syntaxes including, various MARC formats, Simple Unstructured Records Syntax (SUTRS), Generic Record Syntax (GRS), OPAC, Summary, Explain, and Extended Services. Access control facility: A Z39.50 facility that allows the server or target database to request authentication of user authorization or a password from the client or user. Application layer: The top layer in the seven–layer Open Systems Interconnection (OSI) Basic Reference Model that manages program to program communication. In a Z39.50 information retrieval session, all interaction between the client software and server software occurs at this level. Attributes: Z39.50 concept to characterize search terms in a Z39.50 query including the access point to search, the type of search term, whether truncation is desired, etc. Attributes specify how the search term is to be treated by the server when executing the search against a target database. Attribute sets: Attribute sets are registered objects that consist of various attribute types (e.g., Use attributes, Relation attributes, and Structure attributes) and the legal attribute values. Z–clients and Z–servers reference an attribute set through its Object Identifier (OID) to share a common understanding of the query. Bib-1 attribute set: A registered attribute set included in the Z39.50 standard that defines six attribute types (i.e., use, relation, position, structure, truncation, and completeness) and assigns values specific to each type. Used for expressing queries for searching bibliographic databases and other information resources. Client: An application or the software that runs on a user’s computer that interacts with a remote server and its associated database(s). Within the context of Z39.50, the Z–client is the software the user uses to communicate with a Z–server. The Z–client initiates a Z39.50 information retrieval session and submits requests to the Z–server. The Z–client software translates the query into Z39.50 messages, contacts the Z–server(s) software on the remote database(s), negotiates the session rules, and receives the records, all behind the user interface. Client/Server: Client/Server is an architecture for representing interaction between software operating on two separate systems. The Z39.50 standard identifies specific roles and responsibilities for both the Z–client and Z–server in performing certain processes in the information retrieval session. Computer communication: The interaction and transmission of data from one computer to another via a telecommunications media. Database record: A structure in a database that may comprise fields that contain information. Element: The smallest unit of information in a record (e.g., a field or subfield) that can be identified for the purpose of information retrieval. (See Schema, Abstract Record Structure) Element set name: A label that specifies and identifies all elements or a subset of database record elements or possible record components requested for retrieval (e.g., "full" or "brief"). Explain facility: A set of Z39.50 services that allow the Z–client to obtain information about the contents and organization of a server system (including databases) and implementation specifications relating to availability, restrictions, and information to facilitate effective information retrieval. The Explain Service allows the user to investigate target database functionality. Extended services facilities: A set of Z39.50 services that define a set of tasks that the client may request the server to perform. Some of these services include the ability of a client to set up periodic queries performed by the server, to save a result set, to order a document, and to perform database maintenance operations. Field: In database systems, fields are the smallest units of information that may be retrieved. Every field has a name, called the field name. A collection of fields is called a record. File: File is a set of related records (e.g., a bibliographic file). Hardware independent: Refers to an application’s ability to operate autonomous from the system’s physical objects (disks, disk drives, display screens, keyboards, printers, boards, and chips). A Z–client provides hardware independence to users for information retrieval from a Z39.50 accessible database without regard to the equipment on which the database is implemented. Information retrieval protocol: A protocol that enables one system acting as origin to conduct a search for records held in the database of another system acting as target, and to retrieve those records that meet the search criteria. Initialization facility: A set of Z39.50 services that allow for the initial exchange of messages between a Z–client and a Z–server to complete initialization and negotiation of a Z39.50 information retrieval session. Establishes the options to be used throughout the remainder of the session, such as language, protocol version, and default character set. It also provides a means for user authentication. Interoperability: The ability of different types of computers, networks, operating systems, and applications to exchange information and use the information that has been exchanged. Open systems: Allow different computer systems with a variety of hardware and software components to communicate and exchange information. Open systems are possible through the use of standards. Origin: In the Z39.50 standard, the term "origin" refers to the application that initiates operations on behalf of a user. For ease of understanding, this document uses the term "Z–client." Origin/Target system: The origin/target system manages the Z39.50 communication between the initiator of the communication (origin system) and the responder (target system). According to the Z39.50 standard, a system can have the role of an origin, target, or both. Open Systems Interconnection (OSI) Basic Reference Model: The OSI Basic Reference Model is an abstract model comprising seven layers concerned with the communication of data between two peer systems or between a client and a server. Messages are passed from one layer to the next based on a reciprocal hierarchical process of data flow. Z39.50 is an application layer (i.e., layer seven) protocol. Peer-to-Peer: Defines a mode of communication between two computers in which the same protocol is used to communicate and perform approximately the same function for their respective computers. In peer-to-peer communication, each computer has equivalent capabilities and responsibilities. Platform: The underlying hardware or software for a system. The term cross–platform defines application, formats, or devices that work on a variety of platforms. Present service: A Z39.50 service that provides the Z–client the ability to request from the Z–server the results of a search. The service handles the representation of data and allows retrieval of records from the result set. Some specifics include requesting specific ranges of search results, specific elements in a record, specific variance of a record, inclusion of other metadata information per record or per element in a record, search term highlighting, and the record syntax in which the retrieval record will be returned. Profiles: A set of implementor agreements specifying the use of a particular standard (or group of standards) to support a particular application, function, community, environment, or class of information. A profile selects options, subsets, values of parameters, etc., where these choices are left open in the standard, and where these selections are necessary to accomplish identified functions. A profile may also specify aspects of client and server behavior that are beyond the scope of the base standards. Purpose of a profile include: (1) to provide a specification for vendors to build to, resulting in products that will interoperate; and (2) to provide a specification that customers may reference for procurement purposes. Protocol: Established agreements on the requirements of how information/data will be made accessible. Communication protocols such as Z39.50 are detailed specifications that establish how computers will communicate over a network by defining the format and meaning of data being exchanged. Protocol data unit: A unit of information (i.e., a Z39.50 message) defined in the protocol specifications that is exchanged by the Z–client and Z–server. Query: Search criteria posed as a question to the server or target database that defines a particular set of records. The query can be a request for a previous result set, or even a request for previous result set with additional restrictions. A query may contain Boolean operators, fielded search terms, proximity searching, weighted search terms, truncation specification, relation specifiers, and generalized pattern matching techniques. Query type: A defined structure for expressing a search. Z39.50 defines several query types, including: Type-0 (defined outside of the standard between two implementors); Type-1 (basic Reverse Polish Notation (RPN) query structure commonly used in Z39.50 implementations); Type-101 (extended RPN query that supports proximity searching). Record syntax: The format in which a retrieval record is returned to the Z–client. Elements of the local database record are packaged up in a specific syntax or format. Registered object: An information object (e.g., an attribute set or a record syntax) that can be referenced through an object identifier (OID). Relation attribute: Descriptors applied to the search term that specifies how the term is to be treated when used in a search. Relation attributes can specify characteristics including: less than, less than or equal to, equal to, greater than or equal to, and greater than and not equal to. Request: An action by which a client invokes an action or process from the server. Resource control facility: A set of Z39.50 services that allow the Z–server to do accounting functions with the Z–client. The Z–server can provide reports to the Z–client on the status of an account and the costs associated with an information retrieval session. Response: An action by which a server indicates it has completed a request procedure. For example, the server can supply basic information about search results such as the search status, the number of records found, query identification number, any explanation of a failed result set, and other information about the result set. Result-set-delete facility: A set of Z39.50 services that allow the Z–client to request the deletion of specific result sets that the server has created. Result-set-name: Refers to the parameter that allows result sets to be referenced, usually with a number identification. This allows for further refinement of search results or for later recall of a result-set by a user. Retrieval facility: Retrieval facility provides the Z39.50 services by which the Z–client can request the Z–server to return records that have been located during a search. (See the Present service.) Retrieval record: The form of the local database record that is actually returned by a Z–server to a Z–client. Scan service: A Z39.50 service that allows clients to scan an ordered term list. Scan provides the client with the ability to browse access point values/search terms available from a database or group of databases. Schemas: A schema provides an abstract view of the structural organization of a database. It defines how the database fields can be labeled unambiguously by the server to develop a common understanding between the Z–client and the Z–server of the information contained in the records of the server database. Search facility: A Z39.50 facility that allows a Z–client to search one or more Z–servers and their associated databases using a wide variety of selection criteria and structured queries to determine what information is available. Search request: A search request is a structured query in a protocol defined search format used when searching one or more databases. Segment service: A Z39.50 service that allows a Z–client to request transmission of abbreviated records, or special packaging of records to accommodate any network issues related to speed and disk space. Server: An information server that provides access to one or more databases or information resources. A server answers requests for information from clients in a networked environment. Sort facility: A Z39.50 facility that allows a Z–client to request that the Z–server arrange a set of search results into a specific order according to client-supplied criteria. Standard: A standard represents an agreed upon response to a recurring problem—perceived, anticipated, or "real," and codifies the response for the purpose of communication. The standard is the result of a problem–solving process. It involves agreements among stakeholders who have an interest in adopting specific responses to the problem. Conformant use of the standard leads to predictable results and a reduction of uncertainty. Structure attribute: Descriptors applied to the term that specifies how the term is to be treated when used in a search. Structure attributes specify characteristics of the search terms including: phrase, word, key, year, normalized date, un–normalized date, normalized name, and un–normalized name. Tag: A label identifying and characterizing the data in a field. It consists of a pair of integers representing a tag type and a tag value and instructions for encoding data. Tagsets: Tagsets refer to the paired tag values and recommended data types for a set of elements. Target: In the Z39.50 standard, the term "target" refers to the application that responds to requests from a Z–client. For ease of understanding, this document uses the term "Z–server." TCP/IP protocols: Transmission Control Protocol (TCP) and Internet Protocol (IP). Two basic communications protocols used to support communication in the Internet. These protocols allow various services among computers not on the same network. Termination facility: A Z39.50 facility that allows either the Z–client or Z–server to end a Z39.50 information retrieval session. Truncation attribute: Descriptors applied to the search term that specifies how the term is to be treated when used in a search. Allows omitting of characters in search terms for example, by permitting right or left truncation of words. Use attribute: Use attributes are descriptors applied to the search term that specifies how the term is to be treated when used in a search. Use attributes correspond to access points, searchable fields, or indexes that can be referenced in the query. User interface: An interface is a set of commands or menus on the client server computer screen through which a user communicates in a search. Z39.50 Implementors Group (ZIG): A forum for implementors of Z39.50 that has overseen the development of Z39.50 since 1990. Z39.50 Maintenance Agency: The official maintainer of the Z39.50 standard located at the Library of Congress.
Sources: Reed, K. (1996). Data Network Handbook: An Interactive Guide to Network Architecture and Operations. New York, NY: Van Nostrand Reinhold. Michael, J. and Hinnebusch, M. (1995). From A to Z39.50: A Networking Primer. Westport, CT: Meckler Media. ANSI/NISO Z39.50-1995, Information Retrieval (Z39.50): Application Service Definition and Protocol Specification. Bethesda, MD: NISO Press, 1995. ZDNet Webopedia Definitions and Links. HTTP://www.zdwebopedia.com. netlingo: The Internet Language Dictionary. HTTP://www.netlingo.com. The CIMI Profile Draft 1-February 1, 1998, The CIMI Profile: Z39.50 Application Profile For Cultural Heritage Information. HTTP://www.cimi.org/products/cimi_products.html#THREE Enhancing the Standard. HTTP://www.cni.org/pub/NISO/docs/Z39.50-brochure. ISO/TC46/SC4 Glossary. HTTP://lcweb.loc.gov/loc/standards/isotc46/sc4glossary.html. Guide to Open Systems Specifications. HTTP://www.ewos.be Technology Reference Guide. HTTP://www.compucom.com/trg/trg3b.html. Metadata Glossary. HTTP://www.bluangel.com/NewsAndInfo/FAQs/glossary.htm. Compiled by William E. Moen <wemoen@jove.acs.unt.edu> and Teresa Lepchenske School of Library and Information Sciences, University of North Texas. May 1998. Reprint by permission only and copies should contain this credit line information. [Teaching] [Research Projects] [Z39.50] [Research Areas] [Publications] |