1-2-2 Relational Model

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1-2-2 Relational Model

Relational model is a data model that represents the relations of data in a two-dimensional tabular form. The entire table is called “relation,” rows and columns that constitute the table are called “tuples” and “attributes (fields)” respectively. · 5 questions

Relational-model table with Student_number, Name, Japanese, Mathematics and English columns. A dashed outline identifies the relation; the second row is marked as a tuple and the Name column as an attribute. All original three rows and scores are preserved. Source text: Figure 4-2 Relational model — p. 249 · Enlarge

In Figure 4-2, values that are actually recorded, such as “2001”, “Masayuki Abe”, “80”, “90”, and “60”, are referred to as occurrence (or instance). In addition, a set of occurrences that an attribute can take is referred to as domain. (Domain may include data types and constraint conditions of attributes.) Therefore, relation is defined as a subset of the direct product of domains. (Direct product: a set operation that obtains all combinations, Subset: a set that is included in a certain set)

Domains Student Number 2001/2002 and Japanese 80/60 produce four ordered pairs by direct product. The subset relation retains pairs (2001,80) and (2002,60). Original multiplication and arrows remain aligned. Source text: Figure 4-3 Definition of relations — p. 249 · Enlarge

The relational model has a close relationship with the set. Therefore, in the relational database that implements a relational model, the database is operated in combination with relational operations (relational algebra) that are specific to relational database and set operations that are based on the concept of set.

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