Ch 2 Flashcards
Data modeling
Data modeling, the first step in designing a database, refers to the process of creating a specific data model for a determined problem domain (a problem domain is a clearly defined are within the real-world environment, with a well-defined scope and boundaries that will be systematically addressed).
Data model
A data model is a relatively simple representation, usually graphical, or more complex real-world data structures. In general terms, a model is an abstraction of a more complex real-world object or event. A model’s main function is to help you understand the complexities of the real-world environment. Database designers use data models to communicate with end users and programmers.
Entity
An entity is a person, place, thing or event about which data will be collected and stored.
Attribute
An attribute is a characteristic of an entity. E.g. a CUSTOMER entity would be described by attributes such as customer last name, customer first name, customer phone number, etc.
Relationship
A relationship describes an association among entities. E.g. a relationship exists between customers and agents that can be described as follows: an agent can serve many customers, and each customer may be served by one agent.
One-to-many (1:M or 1..*) relationship
E.g. a painter creates many different paintings, but each is painted by only one painter.
Many-to-many (M:N or ..) relationship
E.g. an employee may learn many job skills, and each job skill may be learned by many employees.
One-to-one (1:1 or 1..1) relationship
E.g. a retail company’s management structure may require that each of its stores be managed by a single employee. In turn, each store manages, who is an employee, manages only a single store.
Constraint
A constraint is a restriction placed on data and are important because they help to ensure data integrity. Constraints are normally expressed in the form of rules: an employee’s salary must have values that are between 6,000 and 350,000.
Business rule
A business rule is a brief, precise and unambiguous description of a policy, procedure or principle within a specific organization.
Hierarchical model
The hierarchical model’s basic logical structure is represented by an upside-down tree. The hierarchical structure contains levels, or segments. A segment is the equivalent of a file system’s record type. The hierarchical model depicts a set of one-to-many relationships between a parent and its children segments.
Network model
In the network model, the user perceives the network database as a collection of records in 1:M relationships. However, unlike the hierarchical model, the network model allows a record to have more than one parent.
Schema
The schema is the conceptual organization of the entire database as viewed by the database administrator.
Subschema
The subschema defines the portion of the database “seen” by the application programs that actually produce the desired information from the data within the database.
Data manipulation language (DML)
A data manipulation language (DML) defines the environment in which data can be managed and is used to work with the data in the database.
