A Relational Model of Data for Large Shared Data Banks

A Relational Model of Data for Large Shared Data Banks Edgar F. Codd

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A Relational Model of Data for Large Shared Data Banks 1970 Communications of the ACM 10.1145/362384.362685 codd1970-relational-model codd1970-relational-model.txt, the project's staged copy 9c15bb2b90986817f7b3cd7a72223432064f7c2e open-access computer-science

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0 spans located by searching the stored text for the quote's exact words, allowing any whitespace between them method Quotation withheld because this record is not cleared for redistribution. data independence in shared data banks Quotation withheld because this record is not cleared for redistribution. formal-model formal-model Quotation withheld because this record is not cleared for redistribution. mechanisms represent data as mathematical relations (tables) decoupled from physical storage, so programs are independent of how data is stored and can be queried with a high-level relational language Quotation withheld because this record is not cleared for redistribution. the range of representation changes achievable without impairing programs is still limited what this limits: the data-independence claim: the range of representation changes THAT CAN BE CHANGED WITHOUT LOGICALLY IMPAIRING SOME APPLICATION PROGRAMS IS STILL QUITE LIMITED Quotation withheld because this record is not cleared for redistribution. The paper deliberately excludes any discussion of how systems supporting the model would be implemented. what this limits: any implementation reading: IMPLEMENTATIONS OF SYSTEMS TO SUPPORT THE RELATIONAL MODEL ARE NOT DISCUSSED Quotation withheld because this record is not cleared for redistribution. Further normalisation operations exist but are left out of the paper. what this limits: the normalisation account as complete: further operations exist and THESE ARE NOT DISCUSSED IN THIS PAPER Quotation withheld because this record is not cleared for redistribution. The proposed data sublanguage is only sketched; neither its linguistic detail nor its implementation is worked out. what this limits: any use of the paper as a specification for a query language: NEITHER THE PURELY LINGUISTIC DETAILS OF SUCH A LANGUAGE NOR THE IMPLEMENTATION PROBLEMS ARE DISCUSSED Quotation withheld because this record is not cleared for redistribution. Checking consistency requires an instantaneous snapshot of possibly very large, highly variable relations, a practical problem the paper does not address. what this limits: the consistency-checking proposal at scale: THERE ARE PRACTICAL PROBLEMS (WHICH WE SHALL NOT DISCUSS HERE) IN TAKING AN INSTANTANEOUS SNAPSHOT OF A COLLECTION OF RELATIONS, SOME OF WHICH MAY BE VERY LARGE AND HIGHLY VARIABLE Quotation withheld because this record is not cleared for redistribution. Following a chain of stored connections to answer a question is stated to be erroneous in general; it is valid only when the target relation IS the natural composition of the links, and only if that holds for all time. what this limits: any answer obtained by following paths through linked records: it is correct only in the very special case that the target relation is the natural composition of the relations traversed, and the phrase 'for all time' must normally be added Quotation withheld because this record is not cleared for redistribution. The normalisation procedure is stated to apply only when the collection of relations already satisfies stated structural conditions. what this limits: the claim that a collection of relations can be normalised: the procedure requires the graph of interrelationships of the nonsimple domains to be a collection of trees Quotation withheld because this record is not cleared for redistribution. A distinction the paper draws is then declared not worth maintaining for the rest of the paper. what this limits: the words 'relation' and 'relationship' anywhere after Section 1: the paper states it will not distinguish them except where being explicit is advantageous Quotation withheld because this record is not cleared for redistribution. modelling data as mathematical n-ary relations queried via predicate calculus, giving data independence Quotation withheld because this record is not cleared for redistribution. relational model relational model Quotation withheld because this record is not cleared for redistribution. normalization normalization Quotation withheld because this record is not cleared for redistribution. data independence data independence Quotation withheld because this record is not cleared for redistribution. connection trap connection trap Quotation withheld because this record is not cleared for redistribution. foreign key foreign key Quotation withheld because this record is not cleared for redistribution. primary key primary key Quotation withheld because this record is not cleared for redistribution. the connection trap - A NAMED ERROR: mistaking the derivation of connections for the derivation of relations, which the paper attributes to a lack of understanding of relational composition Quotation withheld because this record is not cleared for redistribution. derivability - HOLDING FOR ALL TIME, not at an instant: because the relations vary in time, the sequence of operations must yield the relation over a significant period, not once Quotation withheld because this record is not cleared for redistribution. data independence - AS INDEPENDENCE FROM TWO THINGS AT ONCE: growth in data types, and changes in data representation, for application programs and terminal activities alike Quotation withheld because this record is not cleared for redistribution. claim_type: method a second reading reaching the same value. Recorded: method — note: A BLIND second reading by the project on 2026-08-25: the record's own claim type/method/phenomenon were not looked at until every value here was written and substring-verified. Not applied - a person decides. Sampling frame: the 504 staged records carrying no alternatives block, so this never re-measures the 202. All 11 records with 130+ tags were taken as a census and 19 more spread one per discipline across 22 disciplines - the dense non-neuroscience cell is the one the 202 do not contain (inside them, 94-100% of the densest bands are neuroscience; among these 11, one is)., Quotation withheld because this record is not cleared for redistribution. method: formal-model a second reading DIFFERING from the recorded value. Recorded: formal-model — note: A BLIND second reading by the project on 2026-08-25: the record's own claim type/method/phenomenon were not looked at until every value here was written and substring-verified. Not applied - a person decides. Sampling frame: the 504 staged records carrying no alternatives block, so this never re-measures the 202. All 11 records with 130+ tags were taken as a census and 19 more spread one per discipline across 22 disciplines - the dense non-neuroscience cell is the one the 202 do not contain (inside them, 94-100% of the densest bands are neuroscience; among these 11, one is)., Quotation withheld because this record is not cleared for redistribution. phenomenon: data independence - insulating application programs from changes in how data is represented a second reading DIFFERING from the recorded value. Recorded: data independence in shared data banks — note: A BLIND second reading by the project on 2026-08-25: the record's own claim type/method/phenomenon were not looked at until every value here was written and substring-verified. Not applied - a person decides. Sampling frame: the 504 staged records carrying no alternatives block, so this never re-measures the 202. All 11 records with 130+ tags were taken as a census and 19 more spread one per discipline across 22 disciplines - the dense non-neuroscience cell is the one the 202 do not contain (inside them, 94-100% of the densest bands are neuroscience; among these 11, one is)., Quotation withheld because this record is not cleared for redistribution. builds-on → n-ary relations and predicate calculus (mathematics/logic) Quotation withheld because this record is not cleared for redistribution. contradicts → the graph or network model of data [3, 4] then in use for noninferential systems Quotation withheld because this record is not cleared for redistribution. builds-on → data description tables in recently developed information systems [5, 6, 7] Quotation withheld because this record is not cleared for redistribution. foreign key —distinct-from→ primary key foreign key primary key the relation itself is separately evidenced · strength of the relation: 1 · the relation stated: a foreign key is DEFINED BY NOT BEING the primary key, while drawing its values from one Quotation withheld because this record is not cleared for redistribution. relational model —causes→ data independence relational model data independence strength of the relation: 1 Audit 2026-09-28: DOUBTFUL - read against its full span and kept, but endpoint by anaphora: 'it' = relational model (previous sentence); the span writes 'maximal independence between programs ... and machine representation', not 'data independence'. Quotation withheld because this record is not cleared for redistribution. 3 — data dependencies still needing removal Quotation withheld because this record is not cleared for redistribution. the relational view appears superior in several respects to the graph or network model Quotation withheld because this record is not cleared for redistribution. the relational model gives a basis for a high-level data language with maximal independence Quotation withheld because this record is not cleared for redistribution. the paper's core problem is data independence Quotation withheld because this record is not cleared for redistribution. the relational view forms a sound basis for treating derivability Quotation withheld because this record is not cleared for redistribution. n-ary relations n-ary relations Quotation withheld because this record is not cleared for redistribution. data representation data representation Quotation withheld because this record is not cleared for redistribution. application programs application programs Quotation withheld because this record is not cleared for redistribution. redundancy and consistency redundancy and consistency Quotation withheld because this record is not cleared for redistribution. relational view (or model) relational view (or model) Quotation withheld because this record is not cleared for redistribution. data independence data independence Quotation withheld because this record is not cleared for redistribution. connection trap connection trap Quotation withheld because this record is not cleared for redistribution.

The full text of this article is not redistributable, so it is not included here. The evidence sentences are withheld with it; the tag layer and its grounding status remain. The article itself is at https://doi.org/10.1145/362384.362685.