GSA (Google Search Appliance) -Collections

1. There is only one Index in GSA (default collection).
2. Collection in GSA is nothing but "view" on the default collection(whole index) based on the URL patterns. To limit search based on URL patterns , you can setup the collection.
3. When the user runs a search , "Site" query parameter decides or identifies which collection it should search against.  (its like post filtering on indexing).
4. If user want to search against specific portion of this index , setup the collection and use site parameter to search  against specific to collection.
5. "site" parameter can set to single collection or against the multiple collections. Following logical operations AND, OR, NOT and grouping can be used like below. eg :
1. To search against single collection products ::: &site=products
2. To search against products AND (intersection operation) services collections ::: &site=products.services
3. To search against products OR (union operation) services ::: &site=products|services
4. To not search in the products ::: &site=-products
5. To search in prices AND (products OR services) ::: &site=prices.(products|services)

6. Creating Collection
1. Goto indexes --> create collection
2. Click on edit on collection, to include or exclude the URL's (URL's you add here must also be in the main index)

7. Few things about the collections
1. You can define as many collections as you want.
2. If you define too many complex queries with collections then there might be performance impact that need to test.
3. You can't define the collections based on the metadata .  But if the documents are organized in separate folder you may try to get the results based on the URL's pattern (collection) and  metdata using the search logical operations.

4. Following is possible, Include URL pattern is like http://sivavaka.com/parent ,  http://sivavaka.com/parent/child/subchild  and exclude pattern is like http://sivavaka.com/parent/child/ .

8. Default Collection: By default when you working with collections in admin console, it includes all collections (/ operator in default collection includes all content in the index)
9. Simple search scenario
1. When user selects specific category and search for the keyword, there is hidden site parameter will specify which collection to use.

Resources

https://developers.google.com/search-appliance/documentation/614