Relevance Ranking Using Terms(Cont.) Most systems add to the above model Words that occur in title,author list,section headings,etc.are given greater importance Words whose first occurrence is late in the document are given lower importance ·Very common words such as“a”,“an”,“the”,“it'etc.are eliminated Called stop words Proximity:if keywords in query occur close together in the document, the document has higher importance than if they occur far apart Documents are returned in decreasing order of relevance score Usually only top few documents are returned,not all Database System Concepts-7th Edition 31.7 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 31.7 ©Silberschatz, Korth and Sudarshan th Edition Relevance Ranking Using Terms (Cont.) ▪ Most systems add to the above model • Words that occur in title, author list, section headings, etc. are given greater importance • Words whose first occurrence is late in the document are given lower importance • Very common words such as “a”, “an”, “the”, “it” etc. are eliminated ▪ Called stop words • Proximity: if keywords in query occur close together in the document, the document has higher importance than if they occur far apart ▪ Documents are returned in decreasing order of relevance score • Usually only top few documents are returned, not all