| The external schema corresponds to the user-level view of the data of the database, one or a few users see the logic of an application-related data that the user application program manipulates data according to external schema. In theory, application program development should focus on the external schema, and are actually for the logic schema at present, not the external schema. Database programming heavy workload characteristics, in order to reduce the workload and improve programmer productivity,to research that subject can be introduced from external schema, which can greatly improve programming efficiency and reduce application development complexity and workload.In the actual development, really valuable is its unique business functions, so developers main energy should concentrate on the development of business systems, but the status quo is that developers spend a lot of time on writing data access and reading or writting operations, a lot of time is wasted in non-business events of the actual process of developing, thus putting the cart before the horse. If external schema on the SQL language extensions, the operation on the subject rather than the traditional table-operation, will make the operation easier, more efficient has important practical significance and research value.In this paper, to study the concept of introducing the subject of the external schema, through research for the subject of the SQL data manipulation language extensions, the new SQL language relating to the operation of subject can make requiring more standardized SQL statement or the more cumbersome data manipulation become easy.To use a series connection of table joining table in querying of a traditional relational database. But to perform querying on the subject, If the information that you want to query on one subject, to make table joining table automatically according to transform of the subject, to achieve query, update operation more efficient and convenient. |
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