From Em Software:
Imagine never having to wonder if your document reflects the latest changes in your database, or whether your database reflects the latest changes made to your document. InCatalog solves the problem by creating transparent links between your documents and databases. An easy-to-use linking palette lets you establish links between elements in the InDesign document and fields in the database file. Once a link is established, InCatalog can update the link immediately. InCatalog lets you update any text or graphics. You can place an InCatalog link on an individual letter, a word, a sentence, a paragraph, or multiple paragraphs, or even whole stories. You can place InCatalog links on graphics and grouped items, allowing you to create or update an entire product module very quickly and easily. You can update parts of the document or the entire document at once, allowing you to change versions, change languages, and even extract data from InDesign documents to build a database. InCatalog is fully bi-directional. Once links are established changes can be made in either the document or the database. When you update, changes are cross-published in the other direction. Linked elements can be moved between documents and libraries freely without loss of linkage. And links don't affect layout or typography.