Editing Logical schema (section)

== History ==
[[Image:4-2 ANSI-SPARC three level architecture.svg|thumb|320px|The ANSI/SPARC [[Three schema approach|three level architecture]], which "shows that a data model can be an external model (or view), a conceptual model, or a physical model. This is not the only way to look at data models, but it is a useful way, particularly when comparing models".<ref name="MW99">Matthew West and Julian Fowler (1999). [http://www.matthew-west.org.uk/documents/princ03.pdf Developing High Quality Data Models] {{webarchive|url=https://web.archive.org/web/20081221084613/http://www.matthew-west.org.uk/documents/princ03.pdf |date=2008-12-21 }}. The European Process Industries STEP Technical Liaison Executive (EPISTLE).</ref> ]]

When ANSI first laid out the idea of a ''logical schema'' in 1975,<ref>American National Standards Institute. 1975. “ANSI/X3/SPARC Study Group on Data Base Management Systems;  Interim Report”.  FDT(Bulletin of ACM SIGMOD) 7:2.</ref> the choices were ''hierarchical'' and ''network''.  The [[relational model]] – where data is described in terms of tables and columns – had just been recognized as a data organization theory but no software existed to support that approach. Since that time, an [[Object-oriented analysis and design|object-oriented]] approach to data modelling – where data is described in terms of classes, attributes, and associations – has also been introduced.