Information Map Studio allows data managers the ability to join tables, create new data elements, and label/format data items for business consumption. However due to this flexibility users must weigh the benefits of customizing information maps against the performance impacts of completing many of these tasks within the Information Map itself.

From anecdotal evidence (in 3.1), I have seen information maps successfully join small tables and display a few custom measures. However, when large tables are joined or a large number of custom measures are utilized, the performance (within Web Report Studio at least) can be dramatically impacted. (Note - I have found that running a test in Information Map for these cases is not indicative of the performance in Web Report Studio.)

So, once all the Web Reports are created and the performance improvements are required, how (in 3.1) can we switch where the custom measure is derived (from an expression within Information Map Studio to a data item in the source table/cube) without crashing the Web Reports?

Two options:

1. You can add these items and modify the associated web reports by hand - or
2. You can modify the XML to ensure that all the web reports use the new item instead.

Included is what a simple calculated expression looks like in the information map XML:
<expr>
<resourceawarestrexpr exprtype="2" scope="2">
<reposobjuse prid="XR1">
<string strvalue="/">
<reposobjuse prid="XR2">
</resourceawarestrexpr>
</expr>

In order to 'trick' the information map into using a different data element, you need to change the entire xml block below into the following:
<Expr>
<ReposObjUse prid="XR3" />
</Expr>

Where the XR3 corresponds to the new data element item in the <ExternalResourceList ...> tagged area added earlier.

Of course - ALWAYS take a backup of the Information Map (and all associated WRS reports) since XML editing can introduce it's own problems.