Imagine you are building a search engine for a retailer website where you need to index fields such as product title, description, sku, category, rating, reviews, and so on. Using a general-purpose analyzer for all these fields may not be the best approach. It would work to some degree but you will soon learn that there are cases where a general-purpose analyzer may return undesired results.

For example, say you have a sku "AB-978" and are using StandardAnalyzer for all fields. The analyzer would break up "AB-978" into two, [ab] [978]. This will have an adverse effect in search accuracy because differences in sku between closely related products may vary very little. We may have another product with sku "AB-978-1". In StandardAnalyzer, both strings would produce these two tokens [ab] [978]. When a user searches for the term "AB-978", both products would be treated with equal weight in the search results. So, there is a possibility that product "AB-978-1" may...