Standard Database: You'll probably never want to look inside your image catalog, but if you ever need to, its your data (or in this case meta-data) and you have a right to it. DigitalPro is based on the same underlying engine as Microsoft Access, so you can always use Access or a compatible database to open the catalog and look at the contents.
There are some tricky issues to consider when you start cataloging your images. The first is Raw Files. You can of course assign keywords or categories to your Raw files in your image catalog, but since Raw files are for the most part undocumented, they are very difficult to caption. Photoshop, for example will not save any File Info to Nikon or Canon Raw files. DigitalPro will save IPTC caption data to Nikon Raw files but not to all Canon Raw file types. PSD files have a similar issue, as they are proprietary to Adobe (although the 8-bit version is documented). Consider using TIFF instead of PSD as your save format instead if you'd rather have an open standard format for your saved images. You can still preserve all your layers.
Creating a good image catalog will take you some work. Personally I wouldn't try to catalog everything at once. You'll probably wind up with a lot of information you won't use and you'll probably forget some key uses of your images that you wish you'd considered. I tend to organize or tag images as I get requests for a particular type of information or as I start to teach a course that requires examples of particular techniques, etc. However you decide to approach the task, having the right software solution is essential. Some key features to look for include: