| 摘要 |
A database application implemented on a computer includes a generic database management product (software) such as IBM DB2 along with a catalog defining the way the data itself is stored. The catalog is a definition of the tables, indexes, views, user authorizations, etc., that specify a user's particular application of the database management system. Access to the database via the catalog uses a structured query language or (SQL) which provides a way of expressing statements in a high-level language so the user will not be burdened with writing code to access the data itself. The structured query language provides statements for defining tables, indexes, views, etc., to be incorporated into the catalog. A database application (to fit a user's business) is generated and updated in a number of phases, such as design, development, test and production, and in each one of these phases a facility exists for making alterations in the database definition (catalog), all of which make use of SQL to implement the changes. According to a feature of the invention, a change definition language (CDL) is provided which is an extension of (and in the general format of) the structured query language. The change definition language allows all important alterations to be described, as changes to an existing definition,for example, and may be used by all phases of the development cycle. The CDL statements do not make the changes directly in the catalog, but instead work through SQL and another intermediate mechanism such as DB2 ALTER tailored to make changes using SQL. The changes expressed in CDL may be migrated to downstream phases and fed back to earlier phases by use of a batch of change statements expressed in CDL.
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