1. Structure of IR Systems INST 734 Module 1 Doug Oard

2. Segments 1.The nature of Information Retrieval (IR) 2.What IR systems do 3.The structure of interactive IR systems

3. Systems: The Memex

4. Types of Information Needs Retrospective (“Retrieval”) –“Searching the past” –Different queries posed against a static collection Prospective (“Recommendation”) –“Searching the future” –Static query posed against a dynamic collection

5. Two Ways of Searching Write the document using terms to convey meaning Author Content-Based Query-Document Matching Document Terms Query Terms Construct query from terms that may appear in documents Free-Text Searcher Retrieval Status Value Construct query from available concept descriptors Controlled Vocabulary Searcher Choose appropriate concept descriptors Indexer Metadata-Based Query-Document Matching Query Descriptors Document Descriptors

6. The IR Black Box Documents Query Hits

7. Inside the IR Black Box Documents Query Hits Representation Function Representation Function Query RepresentationDocument Representation Comparison Function Index

8. Comparison Function Representation Function Query Formulation Human Judgment Representation Function Retrieval Status Value Utility Query Information NeedDocument Query RepresentationDocument Representation Query Processing Document Processing

9. Relevance Relevance relates a topic and a document –Duplicates are equally relevant, by definition –Constant over time and across users Pertinence relates a task and a document –Accounts for quality, complexity, language, … Utility relates a user and a document –Accounts for prior knowledge

10. Comparing Databases and IR Nature of the content Interaction with system Results we get Queries we’re posing What we’re retrieving IRDatabases Updates can often be processed offline. Able to handle real-time updates. Interaction sequence can help resolve vagueness. Single query produces a complete answer. Sometimes relevant, often not. Exact. Always correct in a formal sense. Vague, imprecise queries (and information needs) Unambiguous formally (mathematically) defined queries. Mostly unstructured. Free text with some metadata. Structured data. Clear semantics based on a formal model.

11. Segments 1.The nature of Information Retrieval (IR) 2.What IR systems do 3.The structure of interactive IR systems