What is the crawler's functionality?
Could someone explain this? Thanks!
From SAP WIKI: Crawler and its function
Program that finds large collections of documents by following hyperlinks in a start document and by recursively applying this procedure in the found documents. If the crawler operates on hierarchically structured repositories it finds document collections by identifying the documents and folders in a start folder and by recursively applying this procedure in the found folders.
In simple words, before you start a search, you need a software to run throught your content database...thats the job of a crawler. The job that identify what the crawler should do...is call an index. Thus, indexing is the "process" for asking cralwer/s to do run throught the content database and put the necessary info ready for search.
I will not repeat more about the TREX crawler and indexing relationship to the Portal KM and its setup as its already posted in the above posts.
Hope that helps.