Recursive relationship database example download

Database Systems Design Part III : Entity-Relationship Modeling - ppt download

recursive relationship database example download

Which of the following entities do you think might be recursive? A. PART . This topic introduces Database Design and Relational Database concepts. Jan 15, Download Database Design Hierarchies and Recursive Relationships; 2. Relationships Objectives This lesson covers the following objectives: • Define and give an example of a hierarchical relationship • Identify the. With careful modeling and an understanding of recursive relationships, you can avoid the redundancy Download the Code icon For example, a car is made up of components such as a steering wheel, a frame, and tires. Figure 1 shows a conceptual data model of the Service entity, which is an entity I created that's.

The ER model refines entities and relationships by including properties of entities and relationships called attributes, and by defining constraints on entities, relationships, and attributes. The ER model conveys knowledge at a high-level conceptual level which is suitable for interaction with technical and non-technical users.

Since the ER model is data model independent, it can later be converted into the desired logical model e. Doe EE E2 null M. Miller PR E6 B. An entity type is the basic concept of the ER model and represents a group of real-world objects that have properties.

recursive relationship database example download

Note that an entity type does not always have to be a physical real-world object such as a person or department, it can be an abstract concept such as a project or job. An entity instance is a particular example or occurrence of an entity type. For example, an entity type is Employee. A entity instance is 'E1 - John Doe'. An entity set is a set of entity instances.

An entity type name is normally a singular noun.

Database Systems Design Part III : Entity-Relationship Modeling

That is, use Person instead of People, Project instead of Projects, etc. The first letter of each word in the entity name is capitalized. Note that colors are irrelevant when representing entity types and all other constructs and are only used for aesthetics. Employee Project 13 Relationship Types A relationship type is a set of meaningful associations among entity types.

Each relationship type is given a name that describes its function. A relationship instance is a particular occurrence of a relationship type that relates entity instances. For example, WorksOn is a relationship type. A relationship instance is that 'E1' works on project 'P1' or E1,P1.

A relationship set is a set of relationship instances. Note that there can be more than one relationship between two entity types. This is an example of a many-to-many relationship. A project can have more than one employee, and an employee can work on more than one project. In UML, the relationship type is represented as a label edge between the two entity types.

The label is applied only in one direction so an arrow indicates the correct way to read it. A relationship type name is normally a verb or verb phrase. The first letter of each word in the name is capitalized. For example, WorksOn is a relationship type of degree two as the two participating entity types are Employee and Project.

Relationships of degree two are binary, of degree three are ternary, and of degree four are quaternary. Relationships of arbitrary degree N are called n-ary. Both UML and classical ER notation use a diamond to represent relationships of degree higher than two. For example, an employee has a supervisor. The supervisor is also an employee. In UML notation, each role has a role name: For example, entity type Employee has attributes name, salary, title, etc. By convention, attribute names begin with a lower case letter.

Each attribute has a domain which is the set of allowable values for the attribute. Different attributes may share the same domain, but a single attribute may have only one domain. For example, salary is a simple attribute.

Simple attributes are often called atomic attributes. An attribute is a composite attribute if it consists of multiple components each with an independent existence. For example, address is a complex attribute because it consists of postcode ,street and city components subattributes. Is the name attribute of Employee simple or Complex?

Database Systems Design Part III : Entity-Relationship Modeling - ppt download

For example, salary is a single-valued attribute. An attribute is a multi-valued attribute if it may have multiple values for a single entity instance. For example, a telephone number attribute for a person may be multivalued as people may have different phone numbers home phone number, cell phone number, etc. A derived attribute is an attribute whose value is calculated from other attributes but is not physically stored.

The calculation may involve attributes within the entity type of the derived attribute and attributes in other entity types. For example, the number attribute uniquely identifies an Employee and is a candidate key for the Employee entity type. A primary key is a candidate key that is selected to identify each instance of an entity type.

The primary key is chosen from a set of candidate keys. For instance, an employee may also have SSN as an attribute. The primary key may be either SSN or number as both are candidate keys. A composite key is a key that consists of two or more attributes. For example, a course is uniquely identified only by the department code 22C and the course number within the department UML notation is nice because it is compact. In the ER model, attributes are ovals with the name of the attribute in the oval, and the oval is connected to its entity type.

There are different types of ovals for the different attribute types key attribute, multivalued, composite. In UML, attributes are listed in the rectangle for their entity. Tags are used to denote any special features of the attributes: For example, the WorksOn relationship type has two attributes: Note that these two attributes belong to the relationship and cannot belong to either of the two entities individually as they would not exist without the relationship.

Both UML and classical ER notation use a diamond to represent relationships of degree higher than two. For example, an employee has a supervisor. The supervisor is also an employee. In UML notation, each role has a role name: For example, entity type Employee has attributes name, salary, title, etc. By convention, attribute names begin with a lower case letter. Each attribute has a domain which is the set of allowable values for the attribute.

Database Systems Design Part III : Entity-Relationship Modeling

Different attributes may share the same domain, but a single attribute may have only one domain. For example, salary is a simple attribute. Simple attributes are often called atomic attributes. An attribute is a composite attribute if it consists of multiple components each with an independent existence. For example, address is a complex attribute because it consists of postcode ,street and city components subattributes. Is the name attribute of Employee simple or Complex?

For example, salary is a single-valued attribute. An attribute is a multi-valued attribute if it may have multiple values for a single entity instance. For example, a telephone number attribute for a person may be multivalued as people may have different phone numbers home phone number, cell phone number, etc. A derived attribute is an attribute whose value is calculated from other attributes but is not physically stored. The calculation may involve attributes within the entity type of the derived attribute and attributes in other entity types.

For example, the number attribute uniquely identifies an Employee and is a candidate key for the Employee entity type. A primary key is a candidate key that is selected to identify each instance of an entity type.

The primary key is chosen from a set of candidate keys. For instance, an employee may also have SSN as an attribute. The primary key may be either SSN or number as both are candidate keys. A composite key is a key that consists of two or more attributes. For example, a course is uniquely identified only by the department code 22C and the course number within the department UML notation is nice because it is compact.

In the ER model, attributes are ovals with the name of the attribute in the oval, and the oval is connected to its entity type. There are different types of ovals for the different attribute types key attribute, multivalued, composite. In UML, attributes are listed in the rectangle for their entity.

Tags are used to denote any special features of the attributes: For example, the WorksOn relationship type has two attributes: Note that these two attributes belong to the relationship and cannot belong to either of the two entities individually as they would not exist without the relationship.

Relationship attributes are represented the same as entity type attributes in the ER model. In UML, there are represented as a separate box connected to the relationship using a dotted line. Each student has an id, name, sex, birth date, and grade.

recursive relationship database example download

Each professor has a name and is in a department. Each department offers courses and has professors. A department has a name and a building location. Each course has a name and number and may have multiple sections. Each section is taught by a professor and has a section number. Students enroll in sections of courses. They may only enroll in a course once and in a single section. Once a student completes a course, they receive a grade. The multiplicity is the number of possible occurrences of an entity type that may relate to a single occurrence of an associated entity type through a particular relationship.

For binary relationships, there are three common types: M 30 One-to-One Relationships In a one-to-one relationship, each instance of an entity class E1 can be associated with at most one instance of another entity class E2 and vice versa. A department may have only one manager, and a manager may manage only one department. Each employee manages zero or one department. A department may have only one manager.

A manager employee may manage only one department. However, E2 can only be associated with at most one instance of entity class E1. A department may have multiple projects, but a project may have only one department.

recursive relationship database example download

A project may be associated with at most one department. A department may have multiple projects. An employee may work on multiple projects, and a project may have multiple employees working on it. Each employee works on zero or more projects. Participation determines whether all or only some entity instances participate in a relationship. Participation can either be optional or mandatory.

recursive relationship database example download

If an entity's participation in a relationship is mandatory also called total participationthen the entity's existence depends on the relationship. Called an existence dependency. A project is associated with one department, and a department may have one or more projects. A project may have only one department. Each project has a department.