General information Coexistence
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Relational SQL program interface → relational data organization (RR)
Via the relational SQL program interface, applications access a p urely relational data
organization. This combination of program interface and data organization w ill be referred
to in the following as an RR combination.
An RR combination is suitable for compatible programs since in this case the pr imary and
foreign keys are administered by the user, as prescribed by the standard, which corre-
sponds to their handling in SESAM/SQL and INFORMIX. Since the data structu res are not
based on set relations, the system cannot ensure referential integrity.
CODASYL program interface → CODASYL data organization (CC)
Via the CODASYL program interface (COBOL-DML or CALL-DML of UDS/SQL), applica-
tions access the CODASYL data structures. This combination of pr ogram interface and data
organization will be referred to in the following as a CC combination.
Coexistence of interfaces and data models
UDS/SQL offers the options just described coexistently, which means that a database
handler can perform the following tasks simultaneously:
– run SQL applications and CODASYL applications
(SQL and CODASYL language elements can even be mixed in one and the same appli-
cation, but not within a transaction),
– process relational data structures and CODASYL data st ructures, and
– support all three of the program-interface/data-organization combinations described
above (RR, RC and CC).
In other words, the UDS/SQL data model incorporates the relational and the CODASYL
data models in such a way that each model can exist independently and that SQL state-
ments can be applied to CODASYL data structures. This is referred to as the coexistence
model, a model that was realized for the first time in UDS/SQL and whic h provides an appli-
cation environment combining the flexibility and simplicity of the relatio nal data model with
the efficiency and performance of network database systems.