Database Midterm


1. What is metadata? Metadata is data about data. An item of metadata may describe an individual datum, or content item, or a collection of data including multiple content items.
2. What are an Entity, a Relationship, and a Relation?
a. Examples of entities are: employee, customer, order, item, student, building, equipment, account, course.
b. A relationship is an association among one or more entities.
c. A relation is what states one to many, many to many, or one to one.
3. Name three disadvantages of a file system not based on relational design:
a. There is no concrete work flow
b. There is no scalability
c. There no clearly defined entities.
4. Go to P 30 Questions 1-4 and 16.
5. What are user views? Why do we need them? Data views set permissions to designated to make sure that only users with the granted rights is allowed to see sensitive rights securely.
6. What is a conceptual and or logical schema?
a. A Conceptual Schema is a map of concepts and their relationships. This describes the semantics of an organization and represents a series of assertions about its nature. Specifically, it describes the things of significance to an organization (entity classes), about which it is inclined to collect information, and characteristics of (attributes) and associations between pairs of those things of significance (relationships).
b. A Logical Schema is a data model of a specific problem domain that is in terms of a particular data management technology. Without being specific to a particular database management product, it is in terms of either (for example, in 2007) relational tables and columns, object-oriented classes, or XML tags.
7. Give examples of business rules that apply to data.
a. professors are allowed to input and modify the marks of the students taking the seminars they instruct, but not the marks of students in other seminars.
b. how to convert a percentage mark (for example, 91 percent) that a student receives in a seminar into a letter grade (for example, A-).
c. All master's degree programs must include the development of a thesis.
d. BR124 Teaching assistants who have been granted authority by a tenured professor may administer student grades.
e. A derivation is a statement derived from other knowledge in the business, such as a mathematical or logical inference involving literals and facts. For example, a derivation is the calculation of a pay check based on work hours minus deductions.
f. A structural assertion is a statement that expresses some aspects of the static structure of the organization. The E-R diagram represents the structural assertion of data entities and attributes, and the relationships among entities.
g. An action assertion is a statement of constraints or control on the action of the organization. It deals with the dynamic aspect of the organization.
Examples of action assertion would include: ''A course must have a course name''; ''A student must have a GPA > 2.2 to pass the course'', or ''A professor can't teach a class unless he is qualified to do so''.
8. What is an Entity Type? An entity type is a person, place, object or event or concept about which the organization wishes to maintain data. Represented by a rectangle.
9. What is an entity instance? Person = employee, Place = Warehouse, Object = Car
10. What is a composite attribute? What is it composed of? Composite attributes, can be broken down into component parts. Example, the address attribute is made up of: street, city, state and zip code. Used if a single key cant uniquely identify the record.
11. What is a multi-valued attribute? skill and phone are multi-valued attributes because you can have more than one. Two tables are needed. For example, for employees with multiple skills we have:
12. What is an associative Entity? An associative entity is an entity type that represents an association between (among) one or more entity types and contains attributes that are peculiar to both entity types .
a. CERTIFICATE
b. Registers
c. An associative entity can be thought of as both an entity and a relationship since it encapsulates properties from both. It is a relationship since it is serving to join two or more entities together, but it is also an entity since it may have its own properties. The associative entity must have identifiers, Primary Keys, for both adjoining tables, but may also contain its own unique identifier and other information about the relationship.