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In computing, the network model is a database model conceived as a flexible way of representing objects and their relationships. Its distinguishing feature is that the schema, viewed as a graph in which object types are nodes and relationship types are arcs, is not restricted to being a hierarchy or lattice.
Bachman diagram of a simple network database
The network model was adopted by the CODASYLData Base Task Group in 1969 and underwent a major update in 1971. It is sometimes known as the CODASYL model for this reason. A number of network database systems became popular on mainframe and minicomputers through the 1970s before being widely replaced by relational databases in the 1980s.
While the hierarchical database model structures data as a tree of records, with each record having one parent record and many children, the network model allows each record to have multiple parent and child records, forming a generalized graph structure. This property applies at two levels: the schema is a generalized graph of record types connected by relationship types (called "set types" in CODASYL), and the database itself is a generalized graph of record occurrences connected by relationships (CODASYL "sets"). Cycles are permitted at both levels.
The chief argument in favour of the network model, in comparison to the hierarchical model, was that it allowed a more natural modeling of relationships between entities. Although the model was widely implemented and used, it failed to become dominant for two main reasons. Firstly, IBM chose to stick to the hierarchical model with semi-network extensions in their established products such as IMS and DL/I. Secondly, it was eventually displaced by the relational model, which offered a higher-level, more declarative interface. Until the early 1980s the performance benefits of the low-level navigational interfaces offered by hierarchical and network databases were persuasive for many large-scale applications, but as hardware became faster, the extra productivity and flexibility of the relational model led to the gradual obsolescence of the network model in corporate enterprise usage.
Historyedit
The network model's original inventor was Charles Bachman, and it was developed into a standard specification published in 1969 by the Conference on Data Systems Languages (CODASYL) Consortium. This was followed by a second publication in 1971, which became the basis for most implementations. Subsequent work continued into the early 1980s, culminating in an ISO specification, but this had little influence on products.
Bachman's influence is recognized in the term Bachman diagram, a diagrammatic notation that represents a database schema expressed using the network model. In a Bachman diagram, named rectangles represent record types, and arrows represent one-to-many relationship types between records (CODASYL set types).
Database systemsedit
Some well-known database systems that use the network model include:
Wikimedia Commons has media related to Network models.
(PDF). 1968-09-03. Archived from the original (PDF) on 2007-10-12.
SIBAS Database running on Norsk Data Servers
November 23, 2023
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This article is about the database model For other uses see Network model disambiguation This article has multiple issues Please help improve it or discuss these issues on the talk page Learn how and when to remove these template messages This article includes a list of references related reading or external links but its sources remain unclear because it lacks inline citations Please help to improve this article by introducing more precise citations October 2008 template removal help This article relies largely or entirely on a single source Relevant discussion may be found on the talk page Please help improve this article by introducing citations to additional sources Find sources Network model news newspapers books scholar JSTOR January 2019 This article may be too technical for most readers to understand Please help improve it to make it understandable to non experts without removing the technical details January 2019 template removal help template removal help In computing the network model is a database model conceived as a flexible way of representing objects and their relationships Its distinguishing feature is that the schema viewed as a graph in which object types are nodes and relationship types are arcs is not restricted to being a hierarchy or lattice Bachman diagram of a simple network databaseThe network model was adopted by the CODASYL Data Base Task Group in 1969 and underwent a major update in 1971 It is sometimes known as the CODASYL model for this reason A number of network database systems became popular on mainframe and minicomputers through the 1970s before being widely replaced by relational databases in the 1980s Contents 1 Overview 2 History 3 Database systems 4 See also 5 References 6 Further reading 7 External linksOverview editWhile the hierarchical database model structures data as a tree of records with each record having one parent record and many children the network model allows each record to have multiple parent and child records forming a generalized graph structure This property applies at two levels the schema is a generalized graph of record types connected by relationship types called set types in CODASYL and the database itself is a generalized graph of record occurrences connected by relationships CODASYL sets Cycles are permitted at both levels The chief argument in favour of the network model in comparison to the hierarchical model was that it allowed a more natural modeling of relationships between entities Although the model was widely implemented and used it failed to become dominant for two main reasons Firstly IBM chose to stick to the hierarchical model with semi network extensions in their established products such as IMS and DL I Secondly it was eventually displaced by the relational model which offered a higher level more declarative interface Until the early 1980s the performance benefits of the low level navigational interfaces offered by hierarchical and network databases were persuasive for many large scale applications but as hardware became faster the extra productivity and flexibility of the relational model led to the gradual obsolescence of the network model in corporate enterprise usage History editThe network model s original inventor was Charles Bachman and it was developed into a standard specification published in 1969 by the Conference on Data Systems Languages CODASYL Consortium This was followed by a second publication in 1971 which became the basis for most implementations Subsequent work continued into the early 1980s culminating in an ISO specification but this had little influence on products Bachman s influence is recognized in the term Bachman diagram a diagrammatic notation that represents a database schema expressed using the network model In a Bachman diagram named rectangles represent record types and arrows represent one to many relationship types between records CODASYL set types Database systems editSome well known database systems that use the network model include IMAGE for HP 3000 Integrated Data Store IDS IDMS Integrated Database Management System Univac DMS 1100 Norsk Data SIBAS Oracle CODASYL DBMS for OpenVMS originally known as DEC VAX DBMS See also editNavigational database Graph databaseReferences editDavid M k 1997 Fundamentals Design and Implementation database processing ed s l Prentice Hall Further reading editCharles W Bachman The Programmer as Navigator Turing Award lecture Communications of the ACM Volume 16 Issue 11 1973 pp 653 658 ISSN 0001 0782 doi 10 1145 355611 362534External links edit nbsp Wikimedia Commons has media related to Network models CODASYL Systems Committee Survey of Data Base Systems PDF 1968 09 03 Archived from the original PDF on 2007 10 12 Network CODASYL Data Model SIBAS Database running on Norsk Data Servers Retrieved from https en wikipedia org w index php title Network model amp oldid 1181320618, wikipedia, wiki, book, books, library,
