The Entity Object
An EO represents a table in simple terms.It defines the tables attributes the data types,validation on the data,the primary keys and what not the entire business logic that needs to be defined for pushing data into the target table.
So the EO serves as the sink for data by validating it and finally storing it in to the tables.
The View Object
The view object in simple terms is the data source.It provides data for interacting with it.A VO can be based on EO's which in case are similar to SQL queries used to extract data,or it can be programatically populated or it can be populated with a static list.
They define the join or the link among EO's and VO's.Association defines link between EO's.They can be considered as PrimaryKey/ForeignKey relationship between tables.
The Viewlink is for a VO.It defines the Join conditions.A viewlink can be based on an association or based on attributes,Basing viewlinks on associations have the same advantage of entity cache and few more which are unveiled later.
The Application Module
The application module packages the VO's and serves as the data control.It creates and manages the database transaction.For ADF Model layer its only Application Module which exposes the data needed by the client.So for an end user the interaction and transactional capabilities are provided by the application module.How ever there are many advanced features which i will explain as we progress.
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