Quote: RM/T augments the relational model with system-assigned surrogates for entities

Quotation Skeleton

The need for unique and permanent identifiers for … the relational model were originally intended for this … actual values of user-controlled keys are determined by … ). (2) Two relations may have user-controlled keys … and yet the entities denoted are the same. … assigned a user-controlled key value or after it … have the important consequence that an equi-join on … solution [refs] is to introduce entity domains which …   Google-1   Google-2

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Additional Titles

Quote: the relational model uses user-defined and user-controlled primary keys as unique and permanent identifiers

Quote: with user-controlled keys, an equi-join on common key values may be different that a join on common entities

Quote: problems with user-controlled keys as permanent surrogates: can be changed, different keys for same entity, entities without keys

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