Complex entities and relationships Case examples are from the book: Lars Fank Databaser Teori og Praksis ISBN

The 7 most important slides in this course! Type of relationshipRelationship degree One-to-many relationshipBinary Many-to-many relationshipBinary One-to-one relationshipBinary Tree structure relationshipUnary Network relationshipUnary Order relationshipUnary Relationship of degree NN-ary

Repetition: One-to-many relationships

Repetition: Many-to-many relations.

In a tree structure relation, each node has at most one parent node.

The organization structure of companies is normally a tree structure.

In a production structure the relationship has data associated.

Different illustrations of tree structure relationships:

How would you implement the tree production structure with relatioship data in the relational model? How is it possible to find all the raw materials of a given product?

In a network relationship, a node may have any number of parents.

Different illustrations of network structure relationships:

Illustrate the contents of the Node and Branche tables for the first two levels of the production structure below.

The left diagram illustrates how to produce both logical and physical products. For example the “Input” relationship to the “Logical processes” should have an attribute that describes how much of the raw materials or semi-products that are normally used in the different processes of a production. The right diagram uses a network structure to illustrate the production process. Which implementation model of the production database do you prefer?

Exercise How would you implement a family tree that may be used to prevent inbreeding of animals.

Database of the ERP production module

Is the formal leadership of an organization a network or a tree structure? Is the informal leadership of an organization a network or a tree structure? Describe other examples of network or tree structures?

Phases in relational database design:

Entities are normally stored in tables together with their attributes. Primary key = Any unique identification attribute may be selected as the primary key. EmployeeIDNameCitySex S1PeterÅrhusMale S2JohnKøbenhavnMale S4MichaelOdenseMale S5ElisabethKøbenhavnFemale Forign key = an attribute that is a primary key in some other table. A relationship from one entity to another may be implemented by storing the primary key of the related entity as a forign key. CitySize Århus København1 mill. Odense

Key definitions: Candidate key =any minimal set of attributes that may be used as a primary key. Determinant key = Candidate key for some of the nonprime attributes. Nonprime attribute = Any attribute that is not part of a candidate key. EmployeeID Size BynavnCity Name S ÅrhusAarhus Pedersen S2 1 mill. KøbenhavnCopenhagen Olsen S Odense Hansen S5 1 mill. KøbenhavnCopenhagen Jensen

Boyce-Codd Normal Form (BCNF): BCNF = If a table has more determinant keys they may all be used as the primary key. The problem with the third normal form (3NF) is that it does not allow more than one candidate key in a table, and that is not acceptable. Determinant key = Candidate key for some of the nonprime attributes. Size BynavnCity ÅrhusAArhus Odense 1 mill. KøbenhavnCopenhagen

Is the employee table on Boyce-Codd Normal Form (BCNF)? Candidate key =any minimal set of attributes that may be used as a primary key. Determinant key = Candidate key for some of the nonprime attributes. Nonprime attribute = Any attribute that is not part of a candidate key. EmployeeID Size BynavnCity Name S ÅrhusAarhus Pedersen S2 1 mill. KøbenhavnCopenhagen Olsen S Odense Hansen S5 1 mill. KøbenhavnCopenhagen Jensen

End of session Thank you !!!