From Dwayne Wright PMP, PMI-ACP, CSM
Certified FileMaker Developer
The discussion of Table Occurrences can be a bit confusing. So hang in there and we will get through it. As I refer to tables in one area and table occurrences in another, you might start to consider them interchangeable. This is not the case but they are definitely chained at the hip together.
As I have mentioned in other discussions, a table is where all the data for a particular entity resides and a FileMaker file can hold multiple tables. One thing I have not discussed yet but will in detail is the relationship graph area. FileMaker provides a graphical interface for defining relationships between tables. When a table appears in this relationship graph area (in the define database dialog box), it is referred to as a table occurrence.
So if you want to define a relationship between a people table and an invoice table. You place a table occurrence for people on the relationship graph, you place a table occurrence for the invoice table and then draw a line in between them. The line will start with a field in the people table and end with a field in the invoice table. The fields you decide to use (called key fields) are the foundation of that defined relationship.
It is not uncommon to need to have than one possible relationship between two tables. When you try to add a table twice to the relationship graph, it will ask you for a unique name for that table occurrence. So you can see that it is possible to have a table represented by multiple occurrences, each with a unique name to identify it. These named occurrences are then used in the many various ways you use relationships in layouts, calculations, scripts and value lists. A table can exist and not appear in the relations graph but it is somewhat rare. A table may appear in the relationship graph many times, each with a difference table occurrence name.
To quickly recap, FileMaker stores data in tables. FileMaker uses a graph like area to set, edit and view relationships between tables. The occurrence of table on the relationship graph is called a table occurrence. Table occurrences NOT TABLES are what you see when using relationship information, setup of layout base tables (discussed later) and other areas. A table may be represented many times on a relationship graph with a unique table occurrence for each representation. This allows you to link a table up to other tables an almost unlimited number of times.
FYI... That last sentence is a very powerful and good thing when used properly. That last sentence can be a nightmare when used improperly. More about that in later discussions.
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© 2007 - Dwayne Wright - dwaynewright.com
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