A relational model of data for large shared data banks
Communications of the ACM
An information algebra: phase 1 report—language structure group of the CODASYL development committee
Communications of the ACM
On the semantics of the relational data model
SIGMOD '75 Proceedings of the 1975 ACM SIGMOD international conference on Management of data
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A multi-level or three-level data model is introduced in DPLS -- Database, Dynamic Program Control and Open-Ended POL Support. The first ievel is logically the highest "Information Structure Model" where "Entity, Attribute and Value" are the bases for formalizing information. A logical database is composed of as many logical subfiles as the number of defined entity types. The second level is the "Data Structure Model" where the logical subfiles are broken down into physical subfiles in consideration of unused space, redundancy, variable length data, access efficiency, security, integrity, maintenance, etc. A physical subfile is a collection of stored records with the simplest rectangular form. The third level is the "Storage Structure Model" where physical subfiles are given the required number of pages in the data sets. These clearly separated three-level data representations produce a high degree of data independence and storage device independence, which support system designers with orthogonal system decomposition.