Structured-Entity-Relationship-Model

The Structured Entity Relationship Modeling (SERM ) purport to extend the data model according to the Entity-Relationship method. It was originally released in 1989 by Elmar Sinz.

Objectives

The data object types in a SERM can be either original or dependent. The dependence can be either unilateral or reciprocal.

Notation

The graphical notation in SER diagrams differs significantly from ER diagrams. The relationship type of ER diagrams is not used, instead there are two new types: Entity-Relationship type (ER- type) and relationship type (R- type). The entity type is still in use (E - type).

Relationships between the types are illustrated as arrows. The cardinality of each relationship determines the arrow used. ( For this purpose, there are different notation, for example the one shown here, but which differs from the original by Sinz presented diagram).

Note that SER diagrams particularly illustrating the relationships between the types. To see this clearly, diagrams are drawn according to the following rules:

  • Edges coming from the left and go to the right ( not vice versa). Types far left are thus independent. Types are right depending on types the left, as soon as an arrow from there enters into the types.
  • SER diagrams can not contain cycles but circles. (A circle is represented by a closed sequence of edges, a cycle is a closed sequence of edges, wherein the edge direction is taken into account ).
  • The edges of a SER -diagram provide information about the relation between the types. Edges with PK for Primary Key and FK for Foreign Key labeled (in this example can not be seen ).

Example data model

  • Customer and articles are independent ( primary ) Entities. Their existence is not dependent on anything else. It should be noted that it is sufficient that a type could be independent in order to draw him as I type. So we modeled the example slightly differently, namely so that an invoice is not connected to a (0, *) but with a (1, *) - edge with the customers, so changes to the arrangement of the types of nothing (!). Only the edge of customer after the invoice is changing, although currently a customer depends as much on account, in the form that a customer is created only if at least one invoice is created.
  • Each order refers precisely to a customer. Orders without customers are inadmissible ( order is ER- type) customers without orders, however, permitted (buyer is E- type).
  • For each job belongs to at least one order item. Order and order item are mutually dependent.
  • Each order item refers to an article. An item can occur in several order items.
  • Each statement refers to exactly one customer. Customers without Invoices are again permitted, but not bills without customers.
  • For each statement belongs at least one invoice item. Invoice and invoice item are mutually dependent.
  • Each invoice item refers to exactly one order item. An order item can not be calculated or not.

Procedure for converting an ER diagram into a diagram SER

If there is an ER diagram in min-max notation, this can be the basis of the following procedure after Staud converted into a SER diagram ( from page 196 below).

Example

The following ER diagram in min-max notation is available:

Characteristics of the graph:

  • A specialist has at least one performance that they can be good. A power belongs to exactly one specialist. ( The company expects very closely with the staff. )
  • A service consists of any number of ingredients, but each ingredient belongs to at least one performance.

After the above procedure can be consequent SER - Create chart:

Of performance and can be an ER - type, as they are connected to a (1,1) edge. The remaining types are then converted 1:1. The edges are derived from the cardinalities in the ER diagram.

Data modeling
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