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.

Ejemplo

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

Tipos de entidad (tgerm2500m000)

To create the entity types, use the Tipos de entidad (tgerm2500m000).

To define an entity type, complete the following steps:

In the Tipos de entidad (tgerm2500m000) session, click New
In the Tipo de entidad field, specify an id for the entity type.
Click Guardar

Field	Description
Key fields for the Detalles de tipo de entidad (tgerm2100s000) session
Paquete propietario	The package to which the entity type is related.
Módulo propietario	The module to which the entity type is related.
Vincular con diagrama	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.
Categoría de tipo de entidad	If you select this check box, the entity type is a physical entity type or a logical entity type related to the Baan package.
Tipo de entidad asociativa	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.

Tablas por tipo de entidad (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 Tablas por tipo de entidad (tgerm4100m000) session.

To start this session:

On the Vistas, Referencias o Acciones menu of the Tipos de entidad (tgerm2500m000) session, click Vincular tablas ERP con tipo de entidad...

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

Relaciones de tipo de entidad (tgerm3500m000)

To list and define entity type relationships, use the Relaciones de tipo de entidad (tgerm3500m000) session. The relationships listed in the Relaciones de tipo de entidad (tgerm3500m000) session have been established between the entity types listed in the Tipos de entidad (tgerm2500m000) session.

To define entity type relationships, in the Detalles de relación de tipo de entidad (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 Relación de entidades de datos field, specify an ID for the relationship.
In the De tipo de entidad field, select the first entity type involved in the relationship.
In the A tipo de entidad field, select the other entity type involved in the relationship.
In the Cardinalidad mínima De - A field, specify the number of possible entities for each entity type of a pairing for the entity type you selected in the De tipo de entidad field.
In the Cardinalidad mínima A - De field, for the entity type you have selected in the A tipo de entidad field, specify the number of possible entities per entity type of a pairing.
Click Guardar

Field	Description
Key fields for the Detalles de relación de tipo de entidad (tgerm3100s000) session
La relación es subtipo	Si esta casilla de verificación está seleccionada,, 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.
Hay relación de base datos física	Si esta casilla de verificación está seleccionada,, the entity-type relationship is between entity types that have tables from the LN data dictionary linked to them.
Tabla asociativa	An LN table used to link two entity types that have a many to many relationship between them
Infinita	Si esta casilla de verificación está seleccionada,, the maximum to-from relationship is infinite.

Diagramas de relación de entidad (tgerm1500m000)

To create and maintain the entity-relationship diagrams, use the Diagramas de relación de entidad (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 Diagrama de relaciones de entidad field, specify an ID for the entity relationship diagram.
In the Propietario 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 A modificar por.
Click Guardar