QualityStage is a product now marketed by IBM as part of the Information Server suite. A description of QualityStage can be uncovered using a website called <a href="http://www.google.com">Google</a>. Here's a link to the search result ranking number 1: <a href="
http://www-306.ibm.com/software/data/in ... tage/">IBM WebSphere QualityStage</a>.
QAS is a series of products used to match and standardise mailing addresses in various locales across the world. Their website, perhaps unsurprisingly, is <a href="
http://www.qas.com/">www.qas.com</a>. I have used QAS-Batch to match and cleanse UK addresses. Rather than provide you with an open address database against which you can match yourself, QAS provide the database in a proprietary binary format along with an API (accessible via C) that enables you to submit candidate addresses against the database. The API tells you the closest match, along with confidence levels, etc. There are other products to perform this process 'live' for integration into CRM systems, SAP, Siebel, etc.
You'll see from the descriptions of the products that they each perform different functions. QualityStage does provide rulesets like CASS, etc against which you can standardise addresses from a limited set of geographical regions. QAS has a much larger range of datasets available, along with all the probabilistic matching rules already defined within the API. I found that the very best results came from using the two products in combination.
I'l leave you to read the respective websites. If you ever plan to integrate utilise DataStage/QualityStage/QAS in a single solution then sling me a messaage - I have written a custom stage which 'wraps' QAS' C-API into something a little easier to use.
I don't know if the user named 'u' has any experience with QAS - You'd have to ask them directly.
John.