My problem ist that I don't want a catalog. My goal ist just to use the IPTC/XMP data.
Catalog applications (or Digital Asset Managers) store the IPTC/XMP (and EXIF) data in a database in order to eliminate the need to constantly look into files for their metadata thus speeding up operations like searches. Without some sort of database search, in order for an application to search for specific values in images on a hard drive it would need to:
1) Scan the directory contents of all sub-directories on the given hard drive and:
2) Identify which directory items are images and:
3) Open each image and parse out the metadata and:
4) Search the parsed metadata for the desired search terms.
The above four steps could take hours on a large hard drive with many images in it. A catalog does the first three steps only once, leaving step 4 to be very fast and efficient.
The Mac version has a "Search" facility because Apple provides a system called Spotlight that keeps track of metadata for all files on one's computer. PM (on the Mac) is able to put it to good use.
-Kirk