Editing Network model

{{Short description|Database model invented by Charles Bachman}}
{{About|the database model}}
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[[File:Bachman order processing model.tiff|thumb|320px|Bachman diagram of a simple network database]]
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 [[database schema|schema]], viewed as a [[graph (discrete mathematics)|graph]] in which object types are nodes and relationship types are arcs, is not restricted to being a hierarchy or [[Lattice graph|lattice]].

The 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 [[minicomputer]]s through the 1970s before being widely replaced by [[relational database]]s in the 1980s.

==Overview==
While the [[hierarchical database model]] structures data as a [[Tree data structure|tree]] of [[Record (computer science)|records]], with each record having one parent [[Record (computer science)|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"). [[cycle (graph theory)|Cycle]]s are permitted at both levels. Peer-to-Peer and Client Server are examples of Network Models.

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 [[Information Management System|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==
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 [[International Organization for Standardization|ISO]] specification, but this had little influence on products.

Bachman's influence is recognized in the term [[Data structure diagram#Bachman diagram|'''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==
Some well-known database systems that use the network model include:
*[[IMAGE (database)|IMAGE]] for [[HP 3000]]
*[[Integrated Data Store]]{{r|rdbmsearlyyearsoh20070612}} (IDS)
*[[IDMS]]<ref name="rdbmsearlyyearsoh20070612">{{Cite interview |interviewer=Burton Grad |title=RDBMS Plenary 1: Early Years  |type=PDF |url=https://archive.computerhistory.org/resources/access/text/2013/05/102702562-05-01-acc.pdf |access-date=2025-05-30 |publisher=Computer History Museum |date=2007-06-12}}</ref> (Integrated Database Management System)
*[[Unisys OS 2200 databases|Univac DMS-1100]]
*Norsk Data SIBAS
*[[Oracle Corporation|Oracle]] CODASYL DBMS for [[OpenVMS]] (originally known as [[Digital Equipment Corporation|DEC]] [[VAX]] DBMS)

==See also==
*[[Navigational database]]
*[[Graph database]]

==References==
David M, k., 1997. Fundamentals, Design, and Implementation. database processing ed. s.l.:Prentice-Hall.

==Further reading==
*[[Charles W. Bachman]], ''The Programmer as Navigator.'' [[Turing Award]] lecture, [[Communications of the ACM]], Volume 16, Issue 11, 1973, pp.&nbsp;653–658, {{ISSN|0001-0782}}, {{doi|10.1145/355611.362534}}

==External links==
{{Commons category|Network models}}
*{{cite web
 |url=http://www.sqlsummit.com/PDF/DatabaseSurvey_CODASYL_1968.pdf
 |title=CODASYL Systems Committee "Survey of Data Base Systems"
 |date=1968-09-03
 |archive-url=https://web.archive.org/web/20071012095137/http://www.sqlsummit.com/PDF/DatabaseSurvey_CODASYL_1968.pdf
 |archive-date=2007-10-12}}
*[https://web.archive.org/web/20060904190944/http://coronet.iicm.edu/wbtmaster/allcoursescontent/netlib/ndm1.htm Network (CODASYL) Data Model]
*[http://www.ndwiki.org/wiki/SIBAS SIBAS Database running on Norsk Data Servers]
{{Database models}}

{{DEFAULTSORT:Network Model}}
[[Category:Database models]]
[[Category:Networks]]