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32 Cards in this Set
- Front
- Back
metadata
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data about data such as table and collumn names and data types
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domain
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the entire range of value names
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delimiters
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punctuation that separates different values
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fixed-length records
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database where every entry is of the same length and thus no delimters (only maybe an offset) is needed.
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indexing
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the process for searching for and numbering/aranging delimiters so that records can be easily accessed in the future
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variable-length records
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records where each entry can have a different lenght and delimters tell you when you have reached a different entry
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entity relationship diagram
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a diagram that shows the relationships within a database.
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repitition structure
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another word for a loop
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selection statement
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command that tells sql to select certain types of data from the database
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list 11 properties of a DBMS
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look up properties of a database management system
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query
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and instruction to retrieve data from databases
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null value
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a value which has not been inserted for whatever reason
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primary key
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a collumn or collumns that contain unique and not null values. This prevents two rows from ever being equal (loss of data integrity)
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foreign key
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a collumn which values are limited to the values of the primary key which it references.
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multi-valued attributes
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collumns that require more than one entry to fill each cell
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principle of atomicity
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idea that only one value should be stored in each cell
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referential integrity
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the idea that all values in a foreign key should reference a value in another table.
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composite primary key
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same as a multi-collumn primary key
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one to many, many to one, or many to many (optional/not optional or mandatory/not mandatory)
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ways of defining how foreign keys refer to entries in the linked table
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bridge table
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a many to one table designed to connect two many to many tables and servers as an intermediate table.
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problems with redundancy
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1. requires more storage space
2. creates three types of anomolies |
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update anomoly
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when updating one record you have to change the corresponding record on other rows. happens with redundant data.
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deletion anomoly
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when deleting some data causes you to loose other usefull information. happens often when data is stored only once.
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insertion anomoly
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when you can insert some data without inserting other data which may not be aplicable. Creates a problem before data is even stored.
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goals of normalization
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minimize redundancy
reduce inconsistency avoid anomalies reduce maintenance |
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relational database
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a database that satisfies the first normal form
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first normal form
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look up requirements for first normal form
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2 types of repeating groups
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1. multiple collumns with similar information
2. mult-valued collumns |
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atomic entries
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when one value is stored in each cell
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normalization rule 2
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all non-primary key items depend on all parts of the primary key
(eliminates partial dependencies) |
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normalization rule 3
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all non-primary key collumns depend only on the primary key (eliminates transitive dependencies)
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5 rules for denormalization
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1. performance with realistic data is no good
2. performance can't be improved with hardware and software improvements 3. software designer understands what he is doing 4. business rules are designed to maintain the redundant data |