What is the Difference between
1) ER MODEL and Relational Model
2) Dense Index and Sparse Index
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1. ER MODEL vs Relational Model?
Entity Relationships
• The entity in entity relationships is a person, place or thing. On the most basic level, entity relationships are comprised of two entities, both a type. For example, consider ordering two people. Both are labeled as an entity type "Person." A "worker-manager" relationship, called "works-for," exists between the two entities where one person is categorized as "worker" and the other as "boss." The "works-for" qualifier defines the relationship between the two entities.
Relational Relationships
• Relational relationships are deeply reliant on predicate logic and a finite set of data. They provide a means for a user to declare a method for querying information from a database and rely on the database management system to retrieve the information. For example, if a log-in "James" is entered into a database management system as a predicate, the system would retrieve the relevant information in the database, such as "Last Name" or "Address."
Differences in Links
• One of the cardinal differences between relational relationships and entity relationships has to do with the explicitness and implicitness of their relationships. In entity relationships, the link is explicitly stated. Person A "works for" Person B. In the relational model, the links are implicit with the database. "James" is linked to "Last Name" and "Address" without a stated linkage.
Differences in Semantic Relationships
• Because of its implicitness, in relational relationships any data table has relation and there is very little meaning or semantics to be derived from what the relation is or should be. With entity relationships, the semantics are identified by the relationship type. In this way, it is much easier to understand the meaning of relationships in entity relationships than relational relationships.
Source: http://www.ehow.com
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