Database Presentation Day 2

Database Presentation Day 2 - The Relational Model...

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vjk - Database Technologies The Relational Model relational database was invented by E. F. Codd at IBM in 1970.
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vjk - Database Technologies It allowed files to be related by means of a common field. In order to relate any two files, they simply need to have a common field, which makes the model extremely flexible Poet Poem
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vjk - Database Technologies The Relational Model The relational database focuses on the logical representation of the data and its relationship rather than physical storage details Tables play a prominent role in the relational model
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vjk - Database Technologies Some Basic Terms Entities- An entity is something about which you want to store data Example: Person, Place, concept or event
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vjk - Database Technologies Entity Set Entity Set- An Entity Set is a named collection of entities that share common characteristics. The name of the entity set reflects its contents Example: STUDENT, FACULTY, etc.
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vjk - Database Technologies Attributes Attributes-Each entity has certain characteristics known as attributes Example: STUDENT entity includes the attributes student registration number, name, grade, dob, etc.
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vjk - Database Technologies Table A table is perceived as a two-dimensional structure composed of rows and columns. A table contains a group of related entities i.e., an entity set A table is also called a relation because the relation model’s creator E F Codd, used the term relation as a synonym for table
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vjk - Database Technologies
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vjk - Database Technologies Characteristics of a Table 1. A table is a two-dimensional structure composed of rows and columns 2. Each table row (tuple) represents a single occurrence within the entity set 3. Each table column represents an attribute, and each column has a distinct name
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vjk - Database Technologies Continued… 1. Each row/column intersection represents a single data value 2. Each table must have an attribute or a combination of attributes that uniquely identifies each row 3. All values in a column must conform to the same data format
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vjk - Database Technologies Continued… 7. Each column has a specific range of values known as the attribute domain 8. The order of the rows and columns is immaterial to the DBMS
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vjk - Database Technologies The Keys relational systems require keys that can uniquely identify the rows of a table A key consists of one or more attributes that determines other attributes
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vjk - Database Technologies Different types of Keys 1.Primary 2.Foreign 3.Candidate 4.Alternate
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