You are implying web. If you eliminate web from your major components, the concepts are the same for building a search engine for any data. Like a product search on a company website might need to crawl through a bunch of internal data sources to build an index of all the products, metadata, etc. and you may want some products ranked higher in results for whatever reason.

I think a major effort, if its not web, is defining a common data structure to represent the varying source data sets.

Edit to add: OP if you want to study this, start smaller than "search the web" and get the major component concepts down. Expanding to the web will involve distributed systems stuff to scale but there's only like a handful of companies doing that yet there are many more companies that need a search engine on in-house data.