Database Reference
In-Depth Information
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KEY TERMS AND DEFINITIONS
Access Path:
is a sequence of projection and de-projection operations applied to a set of elements
possibly with intermediate constraints. Access path is used for logical navigation and retrieval of related
data elements.
Concept:
is a data modeling and programming construct which is defined as a couple of one identity
class and one entity class. Concept instances are identity-entity couples. Concepts generalize conventional
classes and are used instead of them for declaring type of elements.
Concept-Oriented Model:
is a model of data which is based on three structural principles: duality
principle postulates that an element is an identity-entity entity couple, inclusion principle postulates that
all elements exist in an inclusion hierarchy, and order principle assumes that all elements are partially
ordered.
Concept-Oriented Query Language:
is a syntactic embodiment of the concept-oriented model. It
is based on a novel data modeling construct, concept, which participates in two relations, inclusion and
partial order. Main operations of this query language are projection, de-projection and product (cube).
De-Projection:
is an operation applied to a set of elements and returning all their lesser elements
which reference the source elements along the specified dimension.
Entity Class:
is one of two constituents of a concept. Its instances are objects which are passed by-
reference using identities. Entity classes are analogous to conventional classes.
Identity Class:
is one of two constituents of a concept. Its instances are values which are passed
by-copy and represent entities. It is assumed that by storing an identity we can always access the rep-
resented entity. Identity classes are used to describe domain-specific address spaces however they can
exist only as part of a concept.
Inclusion Relation:
is used to specify a super-concept this concept is included in. Inclusion relation
among concepts generalizes inheritance relation among classes.
Projection:
is an operation applied to a set of elements and returning all their greater elements which
are those referenced by the source elements along the specified dimension.
