Business rules are constraints or definitions created by an aspect of an organization. They can be applied to almost every aspect of a business and are intended to describe the operation of a business. An example of a business rule could be that no credit check should be done for returning customers. This example would change the design of a database for an automotive company. Domain or health rules specify that all columns in a database must be declared for a defined domain. A domain is a fixed value of the same type of value. Other constraints include non-zero and unique constraints. The non-NULL constraint can be placed in a column to ensure that each row in the table has a value for that column. The uniqueness constraint is a constraint on a column to ensure that there are no duplicate values for that column. Referential integrity: Requires a foreign key to have a matching primary key or be null. Entity integrity: Requires each table to have a primary key; Neither the primary key nor any part of it must contain null values The referential integrity constraint indicates that the customer ID (CustID) in the Order table must match a valid CustID in the Customer table. Most relational databases have declarative referential integrity. In other words, when tables are created, referential constraints are established.

See Figure 9.11 for an example of using only the mandatory symbol. In MS Access, referential integrity is established by binding the PK of the Customer table to the CustID of the Order table. “The” is used to refer to a specific article to show that the article is specific: “The book is on the table”, for example. We can physically see that a book is on a table, and that`s why we call them “the book” and “the table.” We can also use “the” to refer to a specific member of a group. Entity integrity occurs when each primary key in a table has a unique value. This ensures that each row is uniquely identified by the primary key. A requirement for entity integrity is that a primary key cannot have a null value. The purpose of this integrity is that each row has a unique identity and that foreign key values can correctly reference primary key values.

Business rules: received by users when collecting queries and used to determine cardinality Database relational integrity rules are very important for good database design. Many RDBMSs (but not all) automatically apply health rules. However, it is much safer to ensure that your application design conforms to entity and reference constraints. Business constraints – sometimes called semantic constraints. These are additional rules specified by users or database administrators. He was the son of the Duke of Nassau. A class can have a maximum of 30 students. A teacher can teach a maximum of 4 courses per semester. An employee cannot participate in more than 5 projects. An employee`s salary may not exceed the salary of his manager. Constraints: logical statements that specify which data values are allowed and which format is appropriate for an attribute Figure 9.12 shows what a one-to-many relationship symbol looks like, where page many is required. Examples of referential integrity constraints in the company`s customer/order database: 11.

The definition of defining is describing the meaning or character of something. An example of a definition is when you tell someone what a word means. An example of a definition is when you set clear rules for living in your home. Verb. For example, if you look at the Order table on the right side of Figure 9.7, you will see that a customer does not need to place an order to be a customer. In other words, the multiple side is optional. To ensure entity integrity, each table must have a primary key. Neither the PMI nor any part of it must contain null values. This is because the null values of the primary key mean that we cannot identify certain rows. For example, in the EMPLOYEE table, Phone cannot be a primary key because some people may not have a phone. Constraints are a very important characteristic in a relational model. In fact, the relational model supports well-defined constraint theory on attributes or tables.

Constraints are useful because they allow a designer to specify the semantics of the data in the database. Constraints are the rules that force the DBMS to verify that the data satisfies semantics. Cardinality: Expresses the minimum and maximum number of entity occurrences associated with a linked entity instance In Microsoft (MS) Access, referential integrity is established by joining the PK of the Customer table to the CustID of the Order table. Figure 9.1 shows a view of the procedure on the Edit Relationships screen in MS Access. Purpose: It is possible that an attribute has NO matching value, but it is impossible to have an invalid entry. Applying the referential integrity rule makes it impossible to delete a row in a table whose primary key has corresponding foreign key values that are required in another table. For example, a customer may not yet have a sales representative assigned (number), but it is impossible to have an invalid sales representative (number). When establishing referential integrity, it is important that PK and FK have the same data types and come from the same domain. Otherwise, RDBMS will not allow membership. The referential integrity constraint indicates that CrsCode in the Class table must match a valid CrsCode in the Course table. In this situation, it is not enough for CrsCode and the class table section to form the PK, we must also apply referential integrity.

Constraints: Rules that force the DBMS to verify that data satisfies semantics Business constraints, sometimes referred to as semantic constraints, are additional rules specified by users or database administrators that can be based on multiple tables.