Using Concepts in Grid Data Organization - Advanced Research on Computer Education, Simulation and Modeling - page 448

(2) Multivalued attribute vs. object class. In grid file, multivalued attributes of an
object class have to be represented as child elements. WSDL and grid mode
cannot specify that a child element is a multivalued attribute of its parent
element.
(3) identifier (ID). WSDL and grid mode cannot specify the identifier of an object
class which appears as a child element and has a many to many relationship with
its parent element. ID and key of WSDL and grid mode respectively, are not
powerful enough to represent the identifier of such object classes.
(4) IDREF or Foreign Key. As WSDL and grid mode cannot represent identifiers
of some object classes, so foreign key or ID reference of such object classes
cannot be specified.
(5) N-ary relationship type. WSDL and grid mode can only specify child elements
of a parent element, such a relationship is the parent-child relationship and it is a
binary relationship type. Ternary relationship types and N-ary relationship types
among object classes cannot be specified by WSDL and grid mode.
(6) Attribute of object class vs. attribute of relationship type. As WSDL and grid
mode do not have the concept of object classes and relationship types (they only
represent the hierarchical structure of elements and attributes), there is no way
to specify whether an attribute of a element is an attribute of the element (object
class) or an attribute of some relationship type involving the element (object
class) and its ancestors (object classes).
(7) View of grid file. Since WSDL and grid mode cannot specify identifiers and at-
tributes of object classes and relationship types, WSDL and grid mode do not
contain concepts to define views of grid file which change the hierarchical order
of object classes (elements) in the original grid file.
The above concepts (1 to 6) can be captured in the CRD-FS mode diagram, and
because of these concepts, we can define a valid grid view which changes the hierar-
chical order of object classes using a swap operator.10 With the concepts captured in
the CRD-FS mode diagram of an grid database, linked pattern queries on the grid
database can be optimized significantly. Using the work we have done with views, we
can guarantee that if a searching changes the hierarchical order of nodes, the concepts
of the output is consistent with the concepts of the grid file. WSDL and grid mode
cannot be used to interpret the output part when the hierarchical ordering of nodes in
the output is different than in the searching part. With the concepts captured by the
CRD-FS data model, we will be able to interpret grid queries correctly and improve
the searching evaluation performance using these concepts.
2 The CRD-FS Data Model
The Object, Relationship, Attribute data model for Semistructured Data (CRD-FS)
has four basic concepts: object classes, relationship types, attributes and references,
and consists of four diagrams: mode diagram, instance diagram, functional depend-
ency diagram and inheritance diagram.In this paper we are concerned with the CRD-
FS mode diagram.
We shows an CRD-FS mode diagram. The rectangles labeled department, course,
and student are the object classes. Attributes name, code and stuNo are the identifiers