| Applies To | |
| Product(s): | OpenPlant PowerPID |
| Version(s): | SELECTseries 3+ |
| Environment: | N/A |
| Area: | N/A |
| Subarea: | N/A |
| Original Author: | Gerd Eichler |
Introduction
It is well known that there is no strong agreement between relational data model and object data model. To bring them into agreement the SchemaMapping was created. It complies data base tables, columns and foreign keys to classes, properties and relationships of object model. All the information is stored in an xml file (called "mapping file"). The mapping file is necessary for the Plant Project DBPlugin. The Plugin is used to read and write data from and to the application database.
The SchemaMappingAPI is a library that represents mapping object model. It proposes mapping items (class maps, relationship maps and property maps) and allows serialization and deserialization of mapping information into the XML document. The library, however does not provide an easy-to-use approach to edit these mapping items. For these purposes the Mapping Extension for the Bentley Class Editor was created.
Schema Mapping Structure
The structure of the Schema Mapping mostly repeats the structure of an Schema. A simplified diagram showing the structure of the schema mapping is on Fig. 1. The main entities of the mapping are corresponding to the main entities in the Schema. Thus SchemaMap relates to an Schema, ClassMap relates to an CClass and PropertyMap relates to an Property.
- ECSchemaMap. This is the root object which aggregates mappings for all classes and relationships
- ECClassMap. Contains all necessary information needed to select, update and delete instances of the corresponding class of the Plant Project DB. It aggregates mappings for properties of the corresponding class.
- ECRelationshipMap. Contains the same information as ClassMap plus mappings for Source and Target relationship constraints.
- ECPropertyMap. Contains table and column or a set of columns that corresponds to an Class property. It also specifies (if necessary) processors that will aggregate several column values into a single one or transforms somehow the original value.
Operations with Schema Mapping and Plant Project Database Mapping Add-in panel
[[Plant Project Database Mappings|Mappings]]