List and describe the 4 components of a database system.

Please include the questions with your answers. Answer in complete sentences where applicable.

    1. A database is a model of a user’s view of the world. We must ask ourselves “How well does it fit the mental models of the people who are going to use the system?” Discuss why it’s important that the model fits the user requirements, even if the developer “knows better.”
    2. Write the SQL SELECT statement to display the property type, rooms, and rent sorted by the Type.

Use the following PROPERTY table to answer the question:

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PropertyID Type Rooms Rent
306 Apt 3 550
308 House 6 1000
325 Apt 4 625
397 Apt 3 550
412 House 7 1250
441 Apt 2 475
    1. Write the SQL SELECT statement to display the average rent of the properties.

Use the following PROPERTY table to answer the question:

PropertyID Type Rooms Rent
306 Apt 3 550
308 House 6 1000
325 Apt 4 625
397 Apt 3 550
412 House 7 1250
441 Apt 2 475
    1. What is normalization?  Explain why it is important.
    2. List and describe the 4 components of a database system.
    3. Give an example of a data constraint and an example of a business rule. Be sure to label which is which so I can tell you know the difference.
    4. Explain the difference between an entity class and an entity instance, and give an example other than those used in the text or the lectures.
    5. Define the term “weak entity” and give an example other than those used in the text.
    6. Define supertype, subtype and discriminator.
    7. Explain the difference between and inclusive subtype relationship and an exclusive subtype relationship.
    8. Using Microsoft Visio 2013 (available through DreamSpark) draw an IE Crow’s Foot E-R diagram for the entities DEPARTMENT and EMPLOYEE. A DEPARTMENT may have more than one EMPLOYEE, but an EMPLOYEE is only assigned to one DEPARTMENT. Assume that a DEPARTMENT does not need to have an EMPLOYEE, but that every EMPLOYEE is assigned to a DEPARTMENT. Include at least three appropriate identifiers and attributes for each entity.
    9. Explain the following crow’s foot E-R diagram. Be sure to include entities, keys, attributes, cardinality. What is the special type of entity represented by COMMISSION_RATE?

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