| Lesson 3 | Information retrieval services |
| Objective | Describe the different categories of information retrieval services. |
Information Retrieval Services
The terms search engine and engine to refer to any service that allows you to compose your own search query. Any service that provides a compiled directory or allows you to perform searches is called a search service or information retrieval service.
As you now are aware, very often the question you will ask before beginning a search is not "Where do I find a search site?" but, rather, "Which one of all these services do I start with?" This is not a trivial question.
A directory, with its smaller number of hand-selected sites, may be more immediately useful than a search engine if you are searching for beginning-level information on a popular topic. A search engine, by its continual automated Web-roaming, may be more useful if you are looking for very specific information or an obscure topic.
Information Retrieval Models
Modeling in Information Retrieval is a complex process aimed at producing a ranking function
A ranking function is a function that assigns scores to documents with regard to a given query .
This process consists of two main tasks:
- The conception of a logical framework for representing documents and queries
- The definition of a ranking function that allows quantifying the similarities among documents and queries
Modeling and Ranking
Information Retrieval systems usually adopt index terms to index and retrieve documents
Index term:
- In a restricted sense: it is a keyword that has some meaning on its own; usually plays the role of a noun
- In a more general form: it is any word that appears in a document
- Retrieval based on index terms can be implemented efficiently
- Also, index terms are simple to refer to in a query
- Simplicity is important because it reduces the effort of query formulation
Retrieval Service Categories