Intended learning outcomes: Explain Breaking up a reflexive n-to-n association, step 3: Merge the generating classes.
Continuation from previous subsection (20.3.8)
Figure 20.3.8.3 shows the final step, namely, merging the two generating classes to the original class. The result yields the typical form, where the original class is connected with the association class via two 1-to-n associations.
Fig. 20.3.8.3 Breaking up a reflexive n-to-n association. Step 3: Merge the generating classes.
Starting from the association “has subordinate,” via the first key person ID all objects are found in the association class that have the entry of the superior and in the second key person ID have the entry of the subordinate as well as the FTE in this subordination. But you are not taken to the other data for the subordinate person. Via the second 1-to-n association, or “is subordinate to,” you then get to the object in the class “person” that corresponds to the subordinate person and it is there that you find the person’s other attributes such as the person’s last name, first name, and so on.
Analogously, you can start out from a subordinate to find all of the subordinate’s superiors with the FTE in this subordination.
As mentioned, in operational information systems of a company the reflexive n-to-n association is typically found. Another example is the structure of a corporate group, when both a holding and the subsidiary companies appear as objects in the same class customer. Even more familiar is its use to model the structure of the bill of material or where-used list (see Figure 17.2.8.2).
Course section 20.3: Subsections and their intended learning outcomes
20.3 Modeling Information Systems in the Data View and Object View
Intended learning outcomes: Present terms such as object, attribute, object class, view, primary and secondary keys. Explain basic concepts such as association, association role and type. Describe the breaking up of an n-to-n association – in particular a reflexive one – and the association class. Disclose the use of the hierarchical constructs for developing a company-wide generic object model.
20.3.1 Object, Attribute, and Object Class
Intended learning outcomes: Differentiate between entity, object, and data record. Differentiate between attribute and data field. Differentiate between object class, file, and table. Explain the class customer as a table in the relational database model.
20.3.2 View and Primary and Secondary Keys
Intended learning outcomes: Produce an overview on the view on a class. Differentiate between primary key and secondary key. Describe characteristics for a “good” primary key. Explain the representation of a class in an object-oriented approach (with example) and the representation of an object.
20.3.3 Association and (Association) Role
Intended learning outcomes: Differentiate between binary association and reflexive association. Explain Abrial’s access function and the example of the association of the classes “book” and “customer” in library systems. Identify the (association) role.
20.3.4 Single-Valued and Multivalued Roles, and Total and Partial Roles
Intended learning outcomes: Differentiate between a single-valued role and a multivalued role. Differentiate between a total and a partial role, or access function.
20.3.5 Association Types
Intended learning outcomes: Differentiate between the 1-to-1 association, the 1-to-n association, the n-to-1 association, and the n-to-n association. Explain various examples of different binary associations.
20.3.6 Breaking up an n-to-n Association; Association Class
Intended learning outcomes: Explain the association class formed by breaking up an n-to-n association into a 1-to-n association and an n-to-1 association.
20.3.7 The Crow’s-Foot Notation and the Common Entity-Oriented Notation
Intended learning outcomes: Describe the commonly used crow’s-foot notation for depicting associations in the entity-oriented approach. Identify the common notation for associations in the entity-oriented approach.
20.3.7b The Reidentification Key and the Object-Oriented Notation
Intended learning outcomes: Explain the Representation of associations in an object-oriented form, as well as the concept of the reidentification key.
20.3.8 Breaking Up a Reflexive n-to-n Association, Step 1: Duplicate, and Step 2: Breakdown
Intended learning outcomes: Explain Breaking up a reflexive n-to-n association, step 1: Duplicate the class to create its two subclasses, and step 2: Classical breakdown of the n-to-n association.
20.3.8b Breaking Up a Reflexive n-to-n Association, Step 3: Merge
Intended learning outcomes: Explain Breaking up a reflexive n-to-n association, step 3: Merge the generating classes.
20.3.9 Using the Hierarchical Constructs Based on Basic Object Classes: The Company-Wide Generic Object Model
Intended learning outcomes: Explain the basic object classes and possible subclasses (specializations) of an industrial company. Describe the concept of a company-wide data model, or generic model.
