database integration with another database management programme

This is really a question of database implementation and outside the scope of Capture CIS as a product, it is just a "consumer" of the database. Generally speaking, you only want one database application managing each database, your stock system needs to be managing the "stock" database and your engineering database should be decoupled from that for use by CIS, not least, because: "things may go wrong" - you don't want your "stock" database affected by updates initiated by engineers; the maintenance of the "stock" database is probably not focused on managing engineering data requirements like Schematic Parts and PCB Footprints and probably won't, in any case, contain fields to store those properties. In terms of maintaining the "stock position" for parts, you could update an "availability" field in you CIS database periodically, typically "overnight" with some database scripting between the databases is a reasonable approach, if you want to get to a "live" update between the databases, you may need the assistance of someone, or some organisation, with database implementation expertise.