Data model: Difference between revisions

Revision as of 00:58, 18 April 2025

Revision as of 00:58, 18 April 2025

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== History ==

One of the earliest pioneering works in modeling information systems was done by Young and Kent (1958),<ref>Young, J. W., and Kent, H. K. (1958). "Abstract Formulation of Data Processing Problems". In: ''Journal of Industrial Engineering''. Nov-Dec 1958. 9(6), pp. 471-479471–479</ref><ref name="JAB07">[[Janis A. Bubenko jr]] (2007) "From Information Algebra to Enterprise Modelling and Ontologies - a Historical Perspective on Modelling for Information Systems". In: ''Conceptual Modelling in Information Systems Engineering''. [[:w:John Krogstie|John Krogstie]] et al. eds. pp 1-181–18</ref> who argued for "a precise and abstract way of specifying the informational and time characteristics of a [[data processing]] problem". They wanted to create "a notation that should enable the [[Systems analyst|analyst]] to organize the problem around any piece of [[computer hardware|hardware]]". Their work was the first effort to create an abstract specification and invariant basis for designing different alternative implementations using different hardware components. The next step in IS modeling was taken by [[CODASYL]], an IT industry consortium formed in 1959, who essentially aimed at the same thing as Young and Kent: the development of "a proper structure for machine-independent problem definition language, at the system level of data processing". This led to the development of a specific IS [[information algebra]].<ref name="JAB07"/>

In the 1960s data modeling gained more significance with the initiation of the [[management information system]] (MIS) concept. According to Leondes (2002), "during that time, the information system provided the data and information for management purposes. The first generation [[database system]], called [[Integrated Data Store]] (IDS), was designed by [[Charles Bachman]] at General Electric. Two famous database models, the [[network data model]] and the [[hierarchical data model]], were proposed during this period of time".<ref>Cornelius T. Leondes (2002). ''Database and Data Communication Network Systems: Techniques and Applications''. Page 7</ref> Towards the end of the 1960s, [[Edgar F. Codd]] worked out his theories of data arrangement, and proposed the [[relational model]] for database management based on [[first-order logic|first-order predicate logic]].<ref>''"Derivability, Redundancy, and Consistency of Relations Stored in Large Data Banks"'', E.F. Codd, IBM Research Report, 1969</ref>

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[[File:Data Flow Diagram Example.jpg|thumb|240px|Data-Flow Diagram example<ref>John Azzolini (2000). [http://ses.gsfc.nasa.gov/ses_data_2000/000712_Azzolini.ppt Introduction to Systems Engineering Practices]. July 2000.</ref>]]

A data-flow diagram (DFD) is a graphical representation of the "flow" of data through an [[information system]]. It differs from the [[flowchart]] as it shows the ''data'' flow instead of the ''control'' flow of the program. A data-flow diagram can also be used for the [[Data visualization|visualization]] of [[data processing]] (structured design). Data-flow diagrams were invented by [[Larry Constantine]], the original developer of structured design,<ref>W. Stevens, G. Myers, L. Constantine, "Structured Design", IBM Systems Journal, 13 (2), 115-139115–139, 1974.</ref> based on Martin and Estrin's "data-flow graph" model of computation.

It is common practice to draw a [[System context diagram|context-level data-flow diagram]] first which shows the interaction between the system and outside entities. The '''DFD''' is designed to show how a system is divided into smaller portions and to highlight the flow of data between those parts. This context-level data-flow diagram is then "exploded" to show more detail of the system being modeled