acis study guide #3

Acis study guide#3 - Database Concepts 1 Define basic database vocabulary including Database a set of related tables An integrated collection of

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Database Concepts 1. Define basic database vocabulary including: Database - a set of related tables. An integrated collection of logically related data elements. A database consolidates many records previously stored in separate files so that a common pool of data serves many applications. Slower than file systems. Table/Entity- objects you want to keep info about. Record- row in a table. Instance of your object/1 instance of data. A collection of related data fields treated as a unit. Field/Attribute- a column/characteristic in your table. Contains data. A data element that consists of a grouping of characters that describe a particular attribute of an entity. Ex: the name field or salary field of an employee. Value- Contents inside a cell. Ex: “Jean” is a value within the row or column. Primary Key- used to uniquely identify each row or record in a table. Has concatenated (one primary key unique # for each record) that uses more than one field. Treats them together. Can never be blank. Each row will have one primary key. A table can only have 1 primary key. Foreign Key- used to link 2 tables together. Ex: Cust. ID is the foreign key in the relationship between customer and order tables. Always have to be looking at 2 tables. One is “Parent”(Can have multiple children) other is “Child”(Can only have one parent record). Exists so we can link it to the Parent table. A table can have one foreign key, no foreign key, or more than 1. Get a new one each time it’s a child in relationship. Foreign key in child record must be primary key in parent record. Metadata- data about your data. Ex: giving columns/rows titles, # of rows/columns. Data describing the structure, data elements, interrelationships, and other characteristics of a database. Able to correct 100’s of different wrong data entries by using metadata to change one and correct them all. More flexible. Ex: Y2K Data Anomalies- likely to occur with unnecessary data entry. Duplication of data entry. Make a database incorrect. Make as simple as possible. 2. How do databases compare to spreadsheets? a. What are the limitations of spreadsheets that are overcome by a database? - In excel, trying to simplify it by putting all data in one table. Not good b/c you have to re-enter names if you have duplicated data entries. Can’t relate tables in spreadsheets. Can’t have 2 tables on one spreadsheet in excel, it violates the simplicity rule. In excel, you have to manually delete or add a record in every table, but in access, the relationship is automatic between every table. Relationships allow us to find stuff easily in every table. b. List other benefits database provide. – Data independence - data is stored different from instructions on how to store that data. Ad-hoc Recording
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This note was uploaded on 04/13/2008 for the course ACIS 1504 taught by Professor Jmlacoste during the Fall '07 term at Virginia Tech.

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Acis study guide#3 - Database Concepts 1 Define basic database vocabulary including Database a set of related tables An integrated collection of

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