The Entity–Relationship Model
| Autor: | Sam Lightstone, Tom Nadeau, Toby J. Teorey, H.V. Jagadish |
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| Rok vydání: | 2011 |
| Předmět: |
business.industry
Computer science Event (relativity) Principal (computer security) computer.software_genre Term (time) Meaning (philosophy of language) Entity–relationship model Artificial intelligence Weak entity Data mining business Data objects Value (mathematics) computer Natural language processing |
| DOI: | 10.1016/b978-0-12-382020-4.00002-1 |
| Popis: | This chapter defines all the major entity-relationship (ER) concepts that can be applied to the conceptual data modeling phase of the database life-cycle. The basic ER model consists of three classes of objects: entities, relationships, and attributes. Entities are the principal data objects about which information is to be collected; they usually denote a person, place, thing, or event of informational interest. A particular occurrence of an entity is called an entity instance or sometimes an entity occurrence. Relationships represent real-world associations among one or more entities, and, as such, have no physical or conceptual existence other than that which depends upon their entity associations. Relationships are described in terms of degree, connectivity, and existence. These terms are defined in the sections that follow. The most common meaning associated with the term relationship is indicated by the connectivity among entity occurrences: one-to-one, one-to-many, and many-to-many. Lastly, attributes are characteristics of entities that provide descriptive detail about them. A particular occurrence of an attribute within an entity or relationship is called an attribute value. |
| Databáze: | OpenAIRE |
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