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See:
Description
Class Summary | |
Association | The Association class is used to link together the properties of two object types. |
CompoundType | The CompoundType class represents types that are built up from SimpleTypes and other CompoundTypes. |
DataType | The DataType class represents the type of a persistently stored datum. |
DDLWriter | DDLWriter |
Element | The Element class is the abstract base class for functionality common to all metadata classes. |
MetadataRoot | The MetadataRoot is a singleton class that serves as an entry point for the metadata system. |
Model | A Model provides a logical namespace for a related set of ObjectTypes and Associations. |
ModelElement | The ModelElement class represents metadata elements that are components of a Model. |
ObjectType | The ObjectType class is a specialized form of CompoundType that supports inheritence. |
ObjectTypeRegistry | Provides a general purpose object type adapter registry, which is aware of the type hierarchy |
Property | The Property class represents one property of a CompoundType. |
SimpleType | The SimpleType class is the base class for all the primative DataTypes that the persistence layer knows how to store. |
Utilities | General static utility methods for the metadata classes. |
Provides a set of classes to store metadata about data object types and the database schema used to persist data objects.
When the system starts up, the persistence layer reads the PDL
files into an Abstract Syntax Tree using the files within com.redhat.persistence.pdl.nodes
. The Abstract Syntax Tree
then populates the classes within this package. These classes are
then used by the operational persistence layer (the classes within the
com.arsdigita.persistence
package) to perform the standard
operations.
The resulting structure is a hierarchy as every item that can be
represented in PDL extends the Element
class. This class stores
general information about object models and is able to output itself
in the form of a PDL file.
The metadata is divided into Model
s. These models act as the
namespace for all of the metadata information (such as object types,
data queries, and data operations). The model itself is composed of
ModelElement
s.
There are two types of ModelElements: Association
and DataType
. The Association model
type holds information for associations between object types. The
DataType model contains both CompoundTypes and SimpleTypes.
SimpleType
s are used to
represent the primitive DataTypes that the persistence layer knows
how to store. For instance, there are SimpleTypes for BigDecimal,
Integer, Date, and String as well as many others. These are used
for describing Properties as well as Attributes defined
within MAP blocks.
A CompoundType
can
be a ObjectType
.
ObjectTypes
provide specific access special events that act on rows within the
tables. Each DataObject
contains a
single ObjectType and that ObjectType is what contains references to
the events allowing the user to easily manipulate data within the
database. An ObjectType is made up of Attributes (columns in the
database), Associations (mappings between database tables), and Events
(A collection of Operations that dictate how information is stored and
retrieved within the database).
A QueryType is composed of a set of Operations and Mapping
s that allow the user
to retrieve arbitrary information from the database.
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