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.
示例

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
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
The Entity Relationship Modeling top-down procedure
实体类型 (tgerm2500m000)

To create the entity types, use the 实体类型 (tgerm2500m000).

To define an entity type, complete the following steps:

  • In the 实体类型 (tgerm2500m000) session, click New
  • In the 实体类型 field, specify an id for the entity type.
  • Click 保存
Key fields for the 实体类型详细资料 (tgerm2100s000) session
FieldDescription
所属 ERP 子系统The package to which the entity type is related.
所属 Infor LN 模块The module to which the entity type is related.
链接至框图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.
实体类型类别If you select this check box, the entity type is a physical entity type or a logical entity type related to the Baan package.
相关实体类型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.

 

按实体类型列出的表 (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 按实体类型列出的表 (tgerm4100m000) session.

To start this session:

  • On the 相应 menu of the 实体类型 (tgerm2500m000) session, click 链接 ERP 表至实体类型...

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

实体类型关系 (tgerm3500m000)

To list and define entity type relationships, use the 实体类型关系 (tgerm3500m000) session. The relationships listed in the 实体类型关系 (tgerm3500m000) session have been established between the entity types listed in the 实体类型 (tgerm2500m000) session.

To define entity type relationships, in the 实体类型关系详细资料 (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 数据实体关系 field, specify an ID for the relationship.
  • In the 自实体类型 field, select the first entity type involved in the relationship.
  • In the 至实体类型 field, select the other entity type involved in the relationship.
  • In the 最小基本关系类型自 - 至 field, specify the number of possible entities for each entity type of a pairing for the entity type you selected in the 自实体类型 field.
  • In the 最小基本关系类型至 - 自 field, for the entity type you have selected in the 至实体类型 field, specify the number of possible entities per entity type of a pairing.
  • Click 保存
Key fields for the 实体类型关系详细资料 (tgerm3100s000) session
FieldDescription
关系为子类型如果选中此复选框，, 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.
存在物理数据库关系如果选中此复选框，, the entity-type relationship is between entity types that have tables from the LN data dictionary linked to them.
相关表An LN table used to link two entity types that have a many to many relationship between them
无限如果选中此复选框，, the maximum to-from relationship is infinite.

 

实体关系图 (tgerm1500m000)

To create and maintain the entity-relationship diagrams, use the 实体关系图 (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 实体关系图 field, specify an ID for the entity relationship diagram.
  • In the 所有者 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 修改者.
  • Click 保存