Data Model
- Model that describes the relationship: Definition
- Data model is an abstract model of itself, is an abstract model of the data itself -
Relational Model
Three elements:
- Data relationships
- Data semantics
- Basic operation (operation relationship): and, the difference, generalized product, selecting the projection
- Extended operations: cross-connection, in addition to
- Consistency constrains
- Entity integrity constraints
- Referential integrity constraints
- User-defined integrity constraints
Foreign Key: other candidate key relationship, R may be a primary or non-primary property attributes.
Similarities and differences between tables and relationships
= = Tuple row record
Column = = = attribute data item field
Domain (domain): a column range, it is a collection of the same data type
Relationship: Cartesian product of a set of domains
Tuple: Relationship between each element (d1, d2, ..., dn) is called an n-tuple
Properties: Relationship between different columns in the same domain may correspond
In order to distinguish between, you must be a name for each column, called properties. n n mesh relationship must have attributes.