Database Reference
In-Depth Information
tribute name a domain, att s associates for each
relation the set of attributes which compose it and
[[ ]] s associates, for each domain, a type of data
and ATT S =∪ R∈ Rs att s (R).
An instance of S is a function δ s : R s —→
R∈Rs (Inst s (R)) such that δ s (R) ∈ Inst s (R) for any
R ∈ R s , where Inst s (R)= P f (dom s (R)) and dom s (R)=
A∈ atts(R) ([[dom s (A)]] s ).
A (relational or object) database is a triplet
(S, K s , δ s ) where S is a schema, K s a set of con-
straints and δ s an instance of S satisfying the
constraints.
The state δ s is called the current state .
of the database schema can be done using a DTD
or an XML schema (Gardarin, 2002).
Let ELEM and DOM be two disjoined sets
describing intuitively the sets of XML elements
and domains.
An XML DB schema using (ELEM, DOM)
is a pair S = ( E s ,DOM s ) associated to three
functions: dom s : E S s → DOM ; att s : E s P f (E s ); and
[[ ]] s : DOM s → TY PES where TYPES indicates the
various types of the considered system type, doms
associates to each name of simple XML element
a domain, att s associates to each XML element
the set of elements it is composed of and [[ ]] s
associates for each domain a type of data.
An instance of S is a function δ s : E S s —→
R∈Rs ([[dom s (E)]] s ) such that δ s (E) ∈ [[dom s (E)]]
s for anyE ∈ E S s .
A (XML) database is a triplet (S, K s , δ s ) where
S is a schema, K s is a set of constraints and δ s is
an instance of S satisfying the constraints. The
state δ s is called current state .An XML DB as a
data source:
Let S = ( E s ,DOM s ) be an XML schema. In our
formal definition of data sources, S can be seen
as a data source as follows:
An Extended-Relational
DB as a Data Source
Let S = ( R s ,ATT s ,DOM s ) be an extended-relational
schema. In our formal approach, S can be seen as
a data source in the following way:
The set of components
C = ATT s ∪ R s a
component c of C has one of the two fol-
lowing forms: c=DB.R.A or c=DB.R with
R ∈R s and A ∈ATT s .
The ref function, makes it possible to iden-
tify the external references in the database,
it is defined as follows:
X ref Y ⇔ X ⊂ ATT s , Y⊂ AT T s and X are an
external reference to Y.
The comp function describes both schema
The set of components
C = E s ; Let us denote
by E S s and E S c the set of the simple elements
and composed elements, respectively.
The
ref relationship, makes it possible to
identify the external references in the da-
tabase, it is defined as follows: X ref Y ⇔
X ⊂ E S s , Y⊂ E S s and X is an external refer-
ence to Y.
The function comp is the function
relations and composed attributes and is
defined in the following way:
comp: ATT s ∪ R s P f (ATT s ∪ R s )
comp(X)=Y ⇔ X ∈R s , Y ⊂ ATT s and Y =
att s (X) or X ∈ ATT s , X is a composed attribute,
and Y ⊂ ATT s , Y is the set of the attributes com-
posing X.
XML model revisited The definition of an
XML database is also done in the following two
steps: first to describe the structure of the objects
of the real world that we want to store (hierarchical
structure schema) and second to define the objects
to represent (database instance). The description
att s .
Note: The originality of our approach is the
ability to represent heterogeneous models in the
same way. A data source can be seen then as a
set of components (simple or composed) and a
set of relationships.
Search WWH ::




Custom Search