| 摘要 |
<p>Apparatus used in a relational data base system to maintain a dependence between a user-defined field in a row of one base table (101) and the state of a set of rows in another base table (101). There are three kinds of dependent fields: a count field (107) which contains a count of the rows in the set, a sum field (105) which is the sum of a field in the rows of the set, and a base copy down field (113) which is a field in the rows of the set which contains a copy of a value in a field in the row of the one base table. The two base tables make up a referenced-referencing pair and the row from the one table has a primary key (103) which is used as a foreign key (111) in the set of rows of the other base table. The apparatus consists of components (313, 306) in the data dictionary which define the user-defined dependent field and the nature of the dependence, including any conditions thereon, and components (319) in the data base system's run time system for maintaining the dependence. Each time the state of a row in the referencing base table is altered, the run time system uses the data dictionary to determine whether there is a user-defined dependent field, and if there is, what kind of dependent field it is. Code in the run time system then reestablishes the dependence as required for the altered row.</p> |
