Are you talking about classic Maximo (Application Designer) or the new role-based applications (Maximo Mobile, Operational Dashboard, Inspection forms, etc.)? You mentioned app.xml which is normally associated with MAF.
For Maximo Mobile apps, there is a concept of a schema (/maximo/oslc/graphite/mobile/schema) that provides you the attributes being fetched. It's still a bit of a matching game going through relationships, child objects in the object structure, etc.
In classic apps, things also often go through relationships, special include datasources, etc. which is tricky
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Steven Shull
Naviam
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