IDEF 1x Notation - Databases: Design

IDEF 1x Notation

This notation has become very popular among developers, and for a long time it has been a standard for database modeling at the logical and physical levels due to the availability on the market of the specialized software for AllFusion ERWin Data Modeler. Integrating with the business process modeling tool, this tool was one of the most preferred tools, enabling to realize almost completely the stage of designing an information system from describing business functions to structuring data and translating the model into a physical database. To work in this notation, the following element designations were defined (Table 2.16).

Table 2.16

Notation of elements in IDEF 1x notation

No. п/п

Designation

Description

1

Entity

Essence with attributes

Attributes

2

Primary Key (RC)

Primary Key

3

Foreign key (FK)

Foreign key

4

Identifying link

5

11 Identifying link

6

Cardinality 1, 1

7

Cardinality 0. N

8

Cardinality 0, 1

Z

9

Cardinality 1, N

P

10

Cardinality exactly A

N *

11

Many-to-many relationships (#M)

12

a

The categorization relationship

A large number of designations allows, using a graphical representation of the model, to provide exhaustive information about data structures and relationships between them. One of the features that also distinguishes many modern database modeling tools is, in contrast to Peter Chen's notation, the integration into a single element of an entity designation and its attributive composition, including an indication of primary and foreign keys.

According to the notation of GOEB 1x, the entity is denoted by its name (Figure 2.56), represented by a noun or a phrase with the main word in the form of a noun, representing the object of the domain, the information about which will be represented in the database table corresponding to the modeled entity. >

Fig. 2.56. Example of an entity designation in IDEF 1x notation

The

An entity of a rectangular shape is formed under the entity name, divided into two parts, where the top part contains the attributes represented by the primary keys, and the lower part contains all other attributes, including foreign keys. To denote the primary key to the attribute name, the abbreviation RK (Primary Key). When a foreign key is designated, the abbreviation "FK (Foreign Key). Thus, the description of the entity contains the necessary minimum set of information about the structure of the information object.

When a foreign key is also a primary key, it is placed, like all primary keys, in the upper part of the attribute description. Being supported by a specialized software, the notation allows the developer to make the entity representation in a more extended version (Figure 2.57), when for most attributes the most elements of their description are indicated: data type, default, sign of empty value storage, etc.

Fig. 2.57. An example of a detailed description of an entity in IDEF 1x notation

The

The notation implies the designation of two types of connections between entities: identifying and not identifying. The difference in these relationships is that with the identifying relationship, the foreign key of the second entity is simultaneously the element of the primary key of this entity, and when using the non-identifying relationship (Figure 2.58), the foreign key of the second entity remains a common attribute and is located in the entity model in the lower region descriptions of attributes.

Fig. 2.58. An example of a non-identifying link in the SHK 1x notation

The

A dotted line is used to indicate a non-identifying link by a notation. In the case of using an identifying link, the developer must apply a solid line.

As well as in other notations, in the notation SHER 1x it is possible to indicate the meaningful filling of the connection and its power (cardinality), which has a corresponding designation and the letter at the end of the link. To denote the multiplicity of entity instances associated with one instance of another entity, a bold dot is formed at the end. Thus, to denote the connection between many-to-many (MM) , the fat point will be placed on both sides of the link (Figure 2.59).

Fig. 2.59. An example of denoting a many-to-many relationship in notation SHER 1x

The

In the designation of a one-to-many relationship (1: DO), a fat dot is placed only at one end of the link, as indicated by the use of multiple instances associated with the first entity, at the end of the connection with which such a point is indicated. However, to indicate the power (cardinality) of the connection, it is not enough to use the dot designation - you still need to specify the appropriate letter designation:

7 - the instance of the first entity can be bound to no more than one instance of the second entity;

P - the instance of the first entity must necessarily be bound to instances of the second entity, assuming that it is possible to communicate with multiple instances;

N - the instance of the first entity must be associated exactly with N instances of the second entity.

If no literal is specified at the end of the link, then such a link indicates the possibility of linking the instance of the first entity to any number of instances of the second entity, allowing the absence of the associated instance of the second entity.

A special case is the one-to-one relationship, the use of which carries one serious danger. The standard 1: 1 communication view involves using a straight line from both ends of the link without any notation, but this representation indicates that the first and second associated entities are required to contain the instance to be bound when creating the instance. if an instance of the first entity is instantiated, it must immediately reference the instance of the second entity, and likewise vice versa. This situation leads to the impossibility of working with the database, since it is impossible to create instances simultaneously in two or more entities (tables).

Therefore, in order to use the 1: 1 identifying link, it is always necessary to accurately determine the entity where the original instances will be located, which will not initially be associated with instances of the second entity, and at the end of the connection you need to specify a white point (Figure 2.60). In the presented example, you first need to create an instance of the client with the account number of the personal account, and then to this personal account specify the legal entity described by the set of data. As a result, it turns out that it is impossible to create a legal entity if the personal account for it is not determined, which is consistent with the features of the domain.

Fig. 2.60. An example of a one-to-one relationship in the SHER 1x notation

The

As in other notations, for the logical model of a database, the categorization relationship (Figure 2.61) can be used in the notation ILE 1x, which has a different designation from other links, including not only communication lines, but also an element illustrating , that the essence-generalization and essence-categories are connected.

The categorization relationship, by virtue of its features, always uses the 1: 1 communication type. which is identifying and involves the use of a foreign key of the entity-category as the primary key obtained from the primary key of the entity-community. Since this type of connection denotes a one-to-one correspondence of instances of entity-community and entity-categories, the presence of other attributes as primary keys in entity-categories is not mandatory, but admissible. The desire to derive other primary keys in the composition of ordinary attributes is based on two factors:

• the primary key in the category entity is initially considered as the only attribute by which each particular instance of the entity can be identified;

• To ensure the uniqueness of the values ​​of any attribute or group of attributes, you can use the mechanism of a unique index, which is focused precisely on the observance of the uniqueness of values ​​for the corresponding attribute.

Fig. 2.61. Example of a categorization relationship notation in the SHER 1x notation

The

As a result of using the notation YUEG 1x in the example considered, the following model can be obtained, illustrating the basic rules for representing the model and using the corresponding elements (Figure 2.62).

This model presents a set of entities that reflect the field of activity in filling the order with goods. In this case, a categorization link is used to separate physical and legal entities as clients using one-to-one communication, identifier and identification links. A meaningful description is defined for each connection, which, according to the rules of notation, should be represented by two verbal forms reflecting the relationship between entities in both directions - from the first entity to the second one and vice versa.

Fig. 2.62. Example of the model in the SHER 1x notation

thematic pictures

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