About Zim Client-Server Applications

In Client-Server applications, you do not have to do anything special to access or manipulate data stored in the SQL database. The data definitions of objects under Zim's control and the data definitions of objects not under Zim's control are exactly the same. To an application, Zim manipulates both in exactly the same way.

The development of a Zim Client-Server application can be performed in isolation from the SQL database; it can in fact take place on an entirely different computing platform. Zim does not have to be connected to the server through the development phase. This "off-line" development capability eliminates the heavy load that can be placed on SQL servers by development activities.

In order to access SQL database tables, Zim must have a definition of the table. The table must be defined in two places: in Zim and in the SQL database. EntitySets and relationships are flagged as being under the control of Zim or under the control of the SQL database. The definitions of those EntitySets and relationships under control of the SQL database are either exported to the SQL database or imported from the SQL database. You must ensure that the definitions in Zim and the SQL database are compatible. Zim's SQL definition interface provides the means to easily import and export definitions.

Figure 1

In Figure 1, the table "Customers" is defined both in Zim and in the SQL database. If "Customers" is defined as a Zim EntitySet or if Zim is running in ZIM mode, then all references to customers are directed to the Zim EntitySet. If, however, "Customers" is defined to be an SQL table and Zim is running in SQL mode (the default), then all references to customers result in the generation of the appropriate SQL code which is sent to the SQL database.

Zim requires that each EntitySet and data relationship to be managed by the SQL database have at least one unique index defined for it. The unique index is a primary key for the SQL table to which the EntitySet or data relationship corresponds. A primary key is necessary to directly access any record (row) of any SQL table. It does this by generating select statements which specify values for the primary key column(s) of the table. For more information, see Primary Keys.