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FMP 7 Demo, Relationship Graph confusion


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Hi all,

I'm not sure if this is the right place for this kind of question, but I'll try to describe it as fully as I can.

I'm receiving an error when using the Relationship Graph in a demo copy of FMP 7 for MacOS X.

The error dialog reads "There cannot be more than one relational path between any two tables in the graph. Another occurrence of one of the tables must be added to the graph." With a text field labeled 'Name of Occurrence:' and populated by the name of one of my Tables with the number 2 appended to it, and the 'cancel' and 'OK' buttons.

I received this error when attempting to add a relationship from one table to another.

Now, it's very possible that I could be ignorant, and breaking some sort of convention or other rule. My previous experience is with mySQL using both the command line and phpMyAdmin. I'm interested in this graphing functionality of FMP7.

My question is "Why did I receive this error message?"

Version: v7.x

Platform: Mac OS X Panther

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Hello Dennis,

Your question gets to the heart of an issue that must be understood before you can make progress with the new relationship structures of FileMaker.

The relationships graph does not deal with tables, but instead, with Table Occurrences (TOs).

Whereas in the past, you may have created several different relationships from one database to another (and given each relationship a different name), now, rather than the relationships themselves having names, you instead create relationships to several separate TOs and you can then differentiate them be referencing them by their different TO names.

The reasons for this don't become obvious until you realize that in the new structure, relationships automatically impute flow-on relationships to all other TOs that are connected to the TO you reference. For example, if invoices is related to LineItems and LinteItems is related to Products and products is related to Prices, the existence of the relationship from Invoices to LineItems also means the following:

1. LineItems is also related to Invoices (all relationships work in both directions)

2. Invoices is also related to Products and also to Prices

3. Products and Prices also relate back to Invoices (again because relationships are bi-directional)

In this way, when referencing a TO, you are also, by implication, referencing a group of other TOs to which it is related. In v7 this is referred to as a Table Occurrence Group (TOG).

If you create a second relationship between Invoices and LineItems, all the imputed flow-on relationships which the existing relationship to LineItems had will not apply to it (though you may set up others).

So what this means is that the Relationships graph is not displaying a strict traditional Entity Relationship Model (ERM), but instead is displaying multiple TOGs, each of which resembles a separate ERM within itself. It is at the point when you create more than one relationship between two given tables that the Relationships graph departs from a conventional ERM and becomes 'multi-dimensional', accommodating more than one TOG (which is liike a separate ERM within itself) within a single model.

So, to return to the original question, the dialog you are referring to is not an error but a prompt. It is offering you the opportunity to establish a separate TO (and thus begin building a new TOG) so that you will then in effect have "more than one ERM" working in parallel within the relationship model for your solution.

It takes a little while to digest this new way of thinking. It provides a very powerful multi-dimensional relationship model which offers possibilities and options which push the envelope of relationship modelling. You need to think in terms of a multi-layered ERM rather than a conventional 'flat' ERM as is more commonly encountered within other applications. You also need to think of the new relationship structures as three dimensional and extensible rather than the finite lists of relationships we've been familiar with in previous versions of FileMaker.

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