Database Difference Report

What a Database Means in the Context of this Report

This report lists the schema differences between two databases. In many situations, databases are compared with the goal of making one identical to the other. In some situations there is no such objective and we simply want to know what, if any, are the differences.

For consistency sake, this report has been designed such that one of the databases is considered to be the reference model and the other is considered to be an actual database that we are working with. The reference model is considered to be a model built by a data modeling tool. The other database is usually the database you are working with, such as your development database. We refer to these two databases as the reference database and the working database respectively.

In this report, the reference database is denoted by the symbol and the working database by the symbol .

In this report, we compare the working database to the reference database with a possible goal of making it look [structurally] like the reference database. That is, we want to make our working database agree with our data model. Thus, if required, changes are applied to the working database to alter it so that it might look identical [in structure] to the reference database.

This report, usually presents the working database on the left and the reference database on the right. Thinking of this in another way, we read left to right [in the western world] and so we may consider that we progress as we move from left to right. Thus we view the working database [on the left] progressing into the reference database [on the right].

The two databases that are compared are snapshots that were taken of one or more schema in a physical database. Usually, these snapshots contain only a subset of all of the schema in the actual physical database. You may consider that these snapshots are a "filtered" view of the actual physical database.

Besides excluding schema, certain object types may have been excluded from the comparison or may have been excluded from one or both of the snapshots.

Perspective

Whether a snapshot appears in the working database or in the reference database depends on your perspective. The reference database is considered to be your reference model.

When differences exist, symbols are used which indicate what needs to be done to the working database to make it agree with the reference database.

Where objects exist in both databases, they are shown as equivalent or not equal. Where objects exist in one database but not in the other, they are shown as being extra in the reference database or absent from the reference database.

What Is Presented

The differences presented depend on the options that you chose when capturing snapshots of your databases. For example, if you omit storage from either snapshot then storage is omitted from the differences report.

Additionally, the presented differences depend on the options chosen when comparing the two snapshots. For example, if you choose not to compare constraint status then constraint status is not compared and is also omitted from the displayed properties in the differences report.

Details are reported only for those objects which are different. The report does not attempt to present details of equivalent objects. Furthermore, objects that exist in one database but not the other are simply indicated as either extra or absent [in the reference database]. Thus, when an object or object type is identical in both databases then it is indicated as equivalent and no further detail is available. Similarly, objects that are extra or absent with respect to the reference database are indicated as such and no further detail is available. When an object type or object differs between databases, it is indicated as not equal and the differences are included in the report.

Images Used to Represent Changes

The following images and colors are used to indicate differences between the working and reference databases:

	Objects are equivalent.
	Objects are different.
	Object is extra in the reference database.
	Object is absent from the reference database.

Note that the symbols indicate the actions to be taken on the object in the working database. Thus a indicates that the object should be added to the working database. Similarly, a indicates that the object is should be removed from the working database. Finally a indicates that the object in the working database should be changed to match its counterpart in the reference database.

When two databases are compared, each of the schema in the working database are compared against a schema in the reference database. When the schema names are identical in the two databases, the mapping is trivial, that is, each schema in the working database is matched against the schema in the reference database which has the same name. In this situation, the schema mapping table will display identical schema names in the working and reference columns.

When the schema names are different in the two databases, it is necessary for the schemas in the working database to be explicitly mapped to the schemas in the reference database. This is necessary so that each schema in the working database can be compared with it's appropriate counterpart in the reference database.

The schema mapping table displays the mappings used for this comparison. It lists each schema in the working database together with the schema in the reference database against which it was matched.