Global Catalog (CAT)
Global Catalogs are the most generic types of catalogs and reside at the highest level of the hierarchy. A global catalog cannot have a base catalog associated with it. This catalog would house all parts and pieces used in your company, regardless of industry, manufacture, or client.
Industry Catalog (IDS)
Industry Catalogs are the second level of the hierarchy. An Industry catalog can have a Global catalog as a base catalog meaning it will pull parts from the Global catalog to be used within. This catalog would be limited to only the parts you would use in a particular industry, (Pharmaceutical, Waste Water, Oil & Gas…)
Company Catalog (CMP)
Company Catalogs are the third and lowest level of the hierarchy. A company catalog can have a Global or Industry catalog as its base catalog. Here you could narrow down your parts to a particular manufacture of parts or a particular client you work with that only purchases certain parts.
Having these levels of hierarchy allows you to work with smaller catalog files for your specs, but will cause more work to keep them all synced together. This extra work could involve adding parts to a Global Catalog and ensuring you sync the Industry or Company catalog with its base catalog to pick up the new pieces. This could also go the other way where you add a part in the Industry or Company catalog and need to sync that back to the Base catalog.
A Base catalog is the external file that a catalog or PRJ file is referencing. If you are using an Industry or Company catalog you can have a Global catalog to pull parts from. When you associate your PRJ or specification to a catalog, this is your base catalog in which you can pull parts from.
A Project Catalog is a cached version of the base catalog each specification is using in the PRJ. This means that only the parts that are used in that specification are shown in the Project catalog for that particular specification. This is what allows you to send a PRJ out to be used in CADWorx Plant and the designers do not need to have access to the catalog to pull parts from.
When modifying your catalogs it is very important to ensure that your Lower level catalogs are always synced with their Base catalog. Given the potential of having 3 levels of catalogs (Company.cmp --> Industry.ids --> Global.cat) this can be cumbersome to ensure they are all synced together and is why it is often recommended to skip the Industry and Company catalog levels.
On the PRJ side, it is also very important to ensure that your PRJ and specifications are synced with their respective Base catalogs.