Introduction to Entity Relationship Modeling

Entity Relationship Modeling gives an insight to the LN application databases and the way in which they are interrelated.

Entity Relationship Modeling is composed of two main building blocks:

Entity types
Entity relationships

These building blocks are interrelated and used in entity relationship diagrams to show the relationships between the permanent storage components. Together with the other components listed below, they let you illustrate the diversity of relationships between the different databases. A group of related diagrams make up an entity relationship model.

Entity type
A person, place, thing, or concept that you want to record information about. An entity type is a group of entities with common attributes and can be part of a diagram, such as Trucks.
Entity
A single occurrence of an entity type; a fact relevant to the company, and about which information is permanently stored. For example: Truck-A and Truck-B.

Three kinds of entities exist:

Logical entity
Entities that have a meaning to the real world and are comprised of one or more physical entities; they are defined on a higher abstraction level.
Physical entity
Database tables of the LN application.
Associative entity
An entity used to link other entities. An associative entity type is only used when there is a many-to-many relationship between two entity types.

Exemple

There could be an M:N relationship between EMPLOYEE and TRUCK regarding maintenance.

This relationship does not show which EMPLOYEE maintains which TRUCK.

There are also other attributes to be considered, such as time spent, part no. and so on.

As a result of the ambiguity regarding the Many-to-many relationship, the associative entity type MAINTENANCE can be defined. (See figure 2).

Associative entity type

Attribute
A fact or non-decomposable piece of information describing an entity type; for example, Number of wheels.
Attribute value
The value of an attribute; for example, 4 wheels.
Relationship
A reason of relevance for associating entities of one or two entity types.
Cardinality
A specification of the number of possible entities for each entity type of a pairing.

The three types of cardinality are as follows:

One-to-One (1:1)
A one-to-one relationship. Only one instance of entity type B can be associated with only one instance of entity type A.
One-to-Many (1:N)
A one-to-many relationship. Multiple instances of entity type B can be associated with only one instance of entity type A.
Many-to-Many (M:N)
A many-to-many relationship. Multiple instances of entity type B can be associated with multiple instances of entity type A and vice-versa.

Within Entity Relationship Modeling, there is no real difference between logical and physical entities.

The Entity Relationship Modeling procedure

There are two different approaches for modeling databases:

The first is the top down approach, which has to be used when physical entity types, entity relationships and entity relationship diagrams have not yet been created. Therefore, you have to manually create and define all entity types and relationships.
The second is reverse engineering, which is a quick way to model entity relationship diagrams because you can select existing database/table definitions for which a diagram will be created automatically. Reverse engineering can only be used in the case of LN.

Carrying out the Entity Relationship Modeling procedure results in a model that shows the relations between different databases.

Figure 14.2 shows the steps in the Entity Relationship Modeling top down procedure.

The Entity Relationship Modeling top-down procedure

Types d'entités (tgerm2500m000)

To create the entity types, use the Types d'entités (tgerm2500m000).

To define an entity type, complete the following steps:

In the Types d'entités (tgerm2500m000) session, click New
In the Type d'entité field, specify an id for the entity type.
Click Enregistrer

Field	Description
Key fields for the Détails du type d'entité (tgerm2100s000) session
Propriétaire de l'application ERP	The package to which the entity type is related.
Propriétaire du module ERP	The module to which the entity type is related.
Lier au diagramme	The entity-relationship diagram into which an entity type is decomposed. At a different level in the DEM-Tool, you can see the entity-type relationship between the current entity type and other entity types.
Catégorie de types d'entités	If you select this check box, the entity type is a physical entity type or a logical entity type related to the Baan package.
Type d'entité associative	If you select this check box, the entity type serves as a link between two other entity types that have a many-to-many relationship between them.

Tables par type d'entité (tgerm4100m000)

To select one or more tables from the Table Definitions (ttadv4526m000) session, and to link those tables to the selected entity type, use the Tables par type d'entité (tgerm4100m000) session.

To start this session:

On the Vues, Références et Actions menu of the Types d'entités (tgerm2500m000) session, click Lier tables BaanERP au type d'entité

One entity type can be linked to several tables. The interdependent relations between these tables are shown at different levels in the Modeler.

Relations entre types d'entités (tgerm3500m000)

To list and define entity type relationships, use the Relations entre types d'entités (tgerm3500m000) session. The relationships listed in the Relations entre types d'entités (tgerm3500m000) session have been established between the entity types listed in the Types d'entités (tgerm2500m000) session.

To define entity type relationships, in the Détails des relations entre types d'entités (tgerm3100s000) session, select the entity types between which relationships are to be established. You can also define the cardinality of the relationship between the selected entity types.

In the case of an M:N relationship, an associative entity type can be created, and a table can be selected from the Table Definitions (ttadv4526m000) session to serve as a link between two entity types.

To define a relationship between two entity types, complete the following steps:

In the Relation interentités field, specify an ID for the relationship.
In the Type d'entitéDe field, select the first entity type involved in the relationship.
In the Type d'entitéA field, select the other entity type involved in the relationship.
In the Cardinalité minimum De - A field, specify the number of possible entities for each entity type of a pairing for the entity type you selected in the Type d'entitéDe field.
In the Cardinalité minimum A - De field, for the entity type you have selected in the Type d'entitéA field, specify the number of possible entities per entity type of a pairing.
Click Enregistrer

Field	Description
Key fields for the Détails des relations entre types d'entités (tgerm3100s000) session
La relation est un sous-type	Si cette case est cochée,, the entity-type relationship is between a subtype and a supertype entity type; it is used to indicate that the supertype’s attribute also applies to the subtype.
Il existe une relation avec la base de données physique	Si cette case est cochée,, the entity-type relationship is between entity types that have tables from the LN data dictionary linked to them.
Table associative	An LN table used to link two entity types that have a many to many relationship between them
Infini	Si cette case est cochée,, the maximum to-from relationship is infinite.

Diagrammes de relations interentités (tgerm1500m000)

To create and maintain the entity-relationship diagrams, use the Diagrammes de relations interentités (tgerm1500m000) session. An entity-relationship diagram is a graphical design of the relational data model structure. The diagram shows a multilevel structure that consists of entity types and entity-type relationships.

To create an entity-type relationship diagram, complete the following steps:

In the Diagramme des relations interentités field, specify an ID for the entity relationship diagram.
In the Propriétaire field, select the LN user who created or is responsible for the entity relationship diagram.
Select who is authorized to modify the diagram by selecting one of the check boxes under Modifiable par.
Click Enregistrer