Term
Who developed the relational model?
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Definition
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Term
Who developed the Entity-Relationship Diagram?
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Definition
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Term
What were the predominant database models prior to the relational model?
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Definition
network (CODASYL) and hierarchical (IMS) |
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Term
What are the characteristics of navigational schemes?
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Definition
*Calculate Records locations based on file beginning location and record data size
*Read record size from record header and “jump” to next record, until desired record is found
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Term
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Definition
| identifies a single row of a table |
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Term
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Definition
| a superkey that has been reduced to the minimal number of cols that still identify unique rows |
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Term
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Definition
| the candidate key chosen to be the “first” table key, often becomes the primary index for access table data |
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Term
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Definition
§Informal
§Ensures that entities are uniquely identified in the database
§Attributes of Entities are unique
§Formal
§No two rows with the same primary key value
§No NULL values in the primary key
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Term
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Definition
| column (or set of columns) that matches the candidate key (usually primary key) of another table |
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Term
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Definition
§Referential Integrity dictates valid values for a Foreign Key:
§Ensures a database connections are valid
§Values must match a value present in the referenced table
§Null Value
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Term
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Definition
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Extracts rows from a product of two tables such that two input rows contributing to any output row satisfy some specified condition. |
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Term
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Definition
| Extracts the matching rows (the join part) of two tables and the “unmatched” rows from both tables. |
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Term
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Definition
Builds a table consisting of all combinations of rows from each of the two input tables
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Term
| Weak Entities / Identifying Relationships |
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Definition
Weak entities have the PK of a strong entity as part/all of their PK
Solid Relationship line for identifying relationships
Diagonal lines in the corner denote weak entities.
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Term
Optional, Mandatory, Functional
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Definition
Minimum cardinality >=1
Optional = Minimum Cardinality = 0
Functional = Maximum Cardinality = 1
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Term
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Definition
Subtypes inherit attributes of supertypes (direct and indirect).
Allows for different attributes for objects in the same table.
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Term
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Definition
Conceptual Model = ERD
Logical Design = Relational Database Tables
Distributed Database = Distribution Schema
Physical Database = Internal Schema/Populate |
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Term
| Generalization Constraints |
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Definition
Disjointness Constrain:Cannot have more than one sub-type.
Completeness Constrain: Must have at least one sub-type. |
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Term
| Procedural vs Non-Procedural |
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Definition
| Procedural language determines WHAT & HOW a process should be done, Non-procedural language is concerned with the WHAT not the HOW. Non-proc languages are those languages where you specify what conditions the answer should satisfy, but not how to obtain it. |
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Term
| Importance of Relational Model |
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Definition
*No longer did we need to know how the information was formatted in order to get the data.
*Every data item had a unique key or one way to get that item that no other item had.
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Term
| Characteristics of Primary Key |
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Definition
§Stable: never change after assigned
§Single purpose: no other purpose
§Good choices: automatically generated values
§Compromise choice for industry practices
§Identify other unique attributes |
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Term
| SELECT Statement Overview |
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Definition
SELECT <list of column expressions>
FROM <list of tables and join operations>
WHERE <list of logical expressions for rows>
GROUP BY <list of grouping columns>
HAVING <list of logical expressions for groups>
ORDER BY <list of sorting specifications>
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