CIS2210 Assignment 1 PDF

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Chelsea Whittemore

CIS2210 Assignment 1 1. Define each of the following terms: a. data – Raw facts, or facts that have not yet been processed to reveal their meaning to the end user. b. field – An alphabetic or numeric character or group of characters that defines a characteristic of a person, place or thing. For example, a persons social security number, address, phone number and bank balance all constitute fields d. file – A named collection of related records. 2. What is data redundancy, and which characteristics of the file system can lead to it? Data redundancy occurs when the same data are stored in multiple places unnecessarily. The use of spreadsheets and tables in different parts of the organization can cause it. 3. What is data independence, and why is it lacking in file systems? Data independence exists when you can change the data storage characteristics without impeding the program's ability to access the data. Any program that accesses a file system's file must tell the computer not only what to do, but how to do it. Consequently, each program must contain lines that specify the opening of a specific type of file, its record specification, and its field definitions. Data dependence makes the file system extremely cumbersome from the point of view of a programmer and database manager. 4. What is a DBMS, and what are its functions? DBMS stands for Database Management System. The DBMS serves as the intermediary between the user and the database. The structure itself is stored within a collection of files and the only way to access the files is through the DBMS. The DBMS receives all application requests and translates them into the complex operations required to fulfill those requests. Some advantages of DMBS are, improved data sharing, improved data security, better data integration, minimized data inconsistency and improved data access. 5. What is structural independence, and why is it important? Structural independence exists when you can change the file structure without affecting the application's ability to access the data. It matters because if it doesn't exist (or is structural dependent) any change to a file's structure (i.e. adding a new field) would require a program to (1) read a record from the original file (2) transform the original data to conform to the new structure's storage requirements (3) write the transformed data into the new file structure and (4) repeat the steps for EVERY single record in the file.

6. Discuss the importance of data modeling. It is a way to represent reality. Data modeling is the blueprint for the database. The database designer uses data models to facilitate the interaction among designers, application programmers, and end users.

7. What is a business rule, and what is its purpose in data modeling? A business rule is a brief, precise, and unambiguous description of a policy, procedure, or principle within a specific organization's environment. Properly written business rules are used to define entities, attributes, relationships, and constraints. Because these components form the basis for a database design, the careful derivation and definition of business rules is crucial to good database design. 8. How do you translate business rules into data model components? As a rule, a noun in a business rule will translate into an entity in the model, and a verb (active or passive) associating nouns will translate into a relationship among the entities. 9. Describe the basic features of the relational data model and discuss their importance to the end user and the designer. A relation (sometimes called a table) as a matrix composed of intersecting rows and columns. Each row in relation is called a tuple. Each column represents as attribute. It also describes a precise set of data manipulation constructs based on advanced mathematical concepts. A relational model as produced an "automatic transmission" database to replace the "standard transmission" databases that preceded it. Its conceptual simplicity set the stage for a genuine database revolution for both end user and designer. 10. Explain how the entity relationship (ER) model helped produce a more structured relational database design environment. The entity relationship model is easier to examine structures graphically than to describe them in text, database designers prefer to use a graphical tool in which entities and their relationships are pictured. 11. Why are entity integrity and referential integrity important in a database? Entity Integrity is important because all primary key entries are unique, and no part of a primary key may be null. Therefore, each row will have a unique identity, and foreign key values can properly reference primary key values. Referential Integrity is important because a foreign key may have either a null entry, as long as it is not a part of its table’s primary key, or an entry that matches the primary key value in a table to which it is related. (Every non-null foreign key value must reference an existing primary key value.) Therefore, it is possible for an attribute not to have a corresponding value, but it will be impossible to have an invalid

entry. The enforcement of the referential integrity rule makes it impossible to delete a row in one table whose primary key has mandatory matching foreign key values in another table.

12. What are the requirements that two relations must satisfy in order to be considered unioncompatible? For two relations to be union-compatible, both must have the same number of attributes and corresponding attributes must have the same domain. The first requirement is easily identified be a cursory glance at the relations' structures. If the first relation has 3 attributes, then the second relation must also have 3 attributes. If the first table has 10 attributes, then the second relation must also have 10 attributes. To satisfy the second requirement for union-compatibility, the first attribute of the first relation must have the same domain as the first attribute of the second relation. The second attribute of the first relation must have the same domain as the second attribute of the second relation. The third attribute of the first relation must have the same domain as the third attribute of the second relation, and so on.

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