P/FDM is accessed either by using the logic programming language PROLOG or by functional query language DAPLEX
(Gray et al., 1990).
The Functional Data Model and the Data Language DAPLEX
, ACM Transactions on Database Systems, 6 (1) 140-173.
1980], SDM [Hammer and McLeod 1981], DAPLEX
[Shipman 1981], SHM+ [Brodie 1984], Gemstone [Maier et al.
The functional data model & the data language DAPLEX
. ACM Trans.
The functional approach was exemplified by the DAPLEX
model (34) and is having an impact on object models coupled with functions such as the Iris model, now available commercially from HewlettPackard in their Open ODB system.
The model and language are generalizations of FQL  and DAPLEX
, and have an implementation that fits ideally with the modularity required by extensible database technologies.
First, several systems that are extensions to the relational model are surveyed, then the functional data model DAPLEX
, the nonnormalized relational model NF.sup.2., and the database system R.sup.2.D.sup.2 that provides abstract data types in the NF.sup.2 model are described.