Question

Consider the employee entity type. 1\. Suppose the company needs to track the names of dependents for each employee. Show the dependent name as a multi-valued attribute. 2\. Modify your ERD to show empDependentName as a composite multi-valued attribute comprising first and last names and middle initials.

Short answer

The dependent names have been represented as the 'empDependentName' under employee entity which is a multivalued attribute. Further, 'empDependentName' is broken down into 'firstName', 'middleInitial', and 'lastName' illustrating it as a composite multivalued attribute.

Step-by-step solution

Model Dependent Name as a Multivalued Attribute

The dependent names can be represented as a multivalued attribute since an employee can have more than one dependents. This can be represented as empDependentName in the ERD of Employee entity. On the diagram, multivalued attributes are usually depicted as double oval.

Model Dependent Names as Composite and Multivalued Attribute

Next, to show the composite nature of the dependent names, break down the empDependentName attribute further into firstName, middleInitial, and lastName. This means that the empDependentName is not just a multivalued attribute, but a composite multivalued attribute. In other words, each instance has several parts. Thus, each dependent doesn’t just have a name; they have a first name, a middle initial, and a last name.

Key concepts

Multivalued Attribute

When modeling data in an Entity-Relationship Diagram (ERD), a multivalued attribute is used to represent an attribute that can have multiple values for a single entity. For example, consider an employee may have several dependents, each with a name. To accurately model this in an ERD, we would use a multivalued attribute called empDependentName for the Employee entity.

The proper notation for a multivalued attribute in an ERD is typically a double oval, setting it apart from single-valued attributes which are represented by a single oval. This double oval visually communicates to anyone reading the diagram that an employee can have zero, one, or many dependents, and accordingly, zero, one, or many names associated with them.

It’s crucial for students to remember that when depicting a multivalued attribute, we need to consider the underlying fact that there could be various instances of that attribute for a single entity. Incorporating multivalued attributes is key to creating a comprehensive and accurate ERD that reflects the real-world complexity of relationships within data.

Composite Attribute

A composite attribute, on the other hand, is an attribute that can be divided into smaller sub-parts, which represent more basic attributes with independent meanings. For example, a full name can be divided into first name, middle initial, and last name. These smaller parts are still related to the same entity but provide a finer level of detail.

In the context of our ERD for the employee entity, empDependentName would be considered a composite attribute if we need to track not just a single name string, but specifically the first names, middle initials, and last names of each dependent.

Representation for a composite attribute in an ERD is usually a large oval, which is then connected to smaller ovals that represent each component of the attribute (first name, middle initial, and last name in this case). This structure helps to ensure that data is captured in a formatted and granular manner, allowing for more precise data handling and reporting.

ERD Notations

The ERD notations are the standardized symbols and structures used to represent entities, attributes, and relationships in an ERD. Understanding these notations is essential for creating clear and universally understandable diagrams.

The most common ERD notations include:

• Entities: Represented by rectangles and named with singular nouns, they define objects or concepts with data stored about them.
• Attributes: Depicted by ovals connected to their entity rectangles, they describe properties or characteristics of an entity. Standard, multivalued, and composite attributes have distinctive symbols as discussed earlier.
• Relationships: Symbolized by diamonds or lines, they demonstrate how entities are associated with one another.
• Primary Key: Often underlined, it identifies the attribute or attributes that uniquely identify an entity instance.
• Cardinality: Descriptors that denote the number of instances of one entity that can be associated with instances of another entity.

These notations provide a common language for database designers, developers, and stakeholders to discuss and document the data models of an organization. Accurate use of ERD notations ensures the effective communication of database structures and is a critical skill for anyone involved in database conceptualization and design.