12. 8Describe how good and weak entity types differ and offer an example of each.
A strong business type can be an entity type which is not existence-dependent on some other enterprise type A weak entity type is usually an business type that is certainly existence-dependent about some other organization type.
Strong organization weak entity Client is strong organization because it currently has principal key and doesn't be based upon any other organization, but the research is weak entity mainly because depends on client entity and doesn't have principal key. (Section 12. 4).
12. 11You must create a conceptual data type of the data requirements for a company that specializes in THIS training. The Company has 31 instructors and will handle about 100 students per workout. The Company presents five modern technology courses, every single of which can be taught with a teaching staff of several instructors. Each instructor is definitely assigned into a maximum of two teaching clubs or can be assigned to do research. Each trainee performs one modern technology course per training session.
(a) Identify the primary entity types for the company.
(b) Identify the main romance types and specify the multiplicity for each and every relationship. State any presumptions you make about the data.
(c) Using your answers for (a) and (b), draw just one ER diagram to represent the information requirements for the company.
Part 13 Expanded Entity-Relationship Modelling
13. 7- Describe the two main restrictions that affect a specialization/generalization relationship. There are two restrictions that may apply to a superclass/subclass relationship known as participation constraints and disjoint constraints.
Involvement constraint decides whether every occurrence inside the superclass must participate as a member of a subclass. A participation constraint can be mandatory or perhaps optional. A superclass/subclass marriage with a obligatory participation identifies that every organization occurrence in the superclass must also be a member of a subclass. A superclass/subclass relationship with optional contribution specifies a member of a superclass do not need to belong to some of its subclasses.
Discompose constraint details the relationship between members with the subclasses and indicates many people possible for a member of a superclass to be a member of one, or more than 1, subclass. The disjoint restriction only is applicable when a superclass has more than one subclass. If the subclasses are disjoint, then a great entity happening can be a member of only one with the subclasses. To represent a disjoint superclass/subclass romance, an ‘Or' is placed following to the engagement constraint inside the curly brackets. If subclasses of a specialization/generalization are not discompose (called nondisjoint), then an entity happening may be an associate of more than one subclass. The participation and disjoint limitations of specialization/generalization are specific giving the next four groups: mandatory and nondisjoint, optional and nondisjoint, mandatory and disjoint, and optional and disjoint.
13. 8- Describe and contrast the concept of aggregation and composition and give an example of each.
Aggregation: signifies a " has a” or " is component of” marriage between entity types, in which one signifies the " whole” and the other the " part”. The relationship presents an association among two organization types which might be conceptually additionally type. Model: Has marriage which corelates the part entity towards the staff business. Branch business is the whole when the staff entity may be the part of the part. See determine 13. 9 for better example.
Composition: a specific sort of aggregation that represents an association between choices, where there can be described as strong control and coincidental lifetime between " whole” and the " part”. Case: the...