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20 Cards in this Set
- Front
- Back
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Database |
Collection of related data |
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Data |
Known facts that can be recorded and have meaning |
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Database Management System |
Software to facilitate the creation/maintenance of a database |
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Database System |
The DBMS with the data itself, and sometimes application |
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Characteristics of Database Approach |
Self-Describing Nature of a Database System Program-Data Independence Data Abstraction Support got Multiple Views of Data Sharing Data/Multi-User Transaction Processing |
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Advantages of Database Approach |
Controlling redundancy Providing multiple interfaces Restricting access Providing backup/recovery services Representing complex relationships Enforcing integrity constraints |
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When a DBMS may be unnecessary |
If DB is simple, well-defined and unlikely to change If concurrent access not required If real-time requirements may be broken by DBMS overhead |
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When a DBMS may not suffice |
If users needs special operations not supported by DBMS If modelling limitations mean complexity of data cannot be handled |
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Data Model |
A set of concepts to describe: Structure of DB Operations for manipulating structures Constraints that DB should obey |
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Data Model Constraints |
Define restrictions on valid data that must be followed at all times |
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Data Model Operations |
Specify DB retrievals and updates by referring to constructs of data model Basic: insert,delete,update User-defined: compute_student_gpa |
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Data Model Categories |
Conceptual Models (high level, semantic) Physical Models (low level, internal) Implementation Models (representational) |
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Schema |
Description of DB, including structure, data types and constraints |
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Schema Diagram |
Illustrative display of schema |
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Schema Construct |
Component of schema or object within it |
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State |
DB, including data, as it exists at a particular moment in time |
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Schema vs State |
Infrequent change vs change every time data is modified |
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Three-Schema Architecture (TSA) |
Supports program-data independence and multiple view of data |
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Three Levels of Schemas in TSA |
Internal Schema (Physical Data Model) - physical storage details Conceptual Schema (Conceptual/ Implementation Model) - structure/constraints of DB External Schema (same as Conceptual Schema) - user views |
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DBMS Languages |
Data Definition Language (DDL) Specifies Conceptual/Internal Schemas Data Manipulation Language (DML) Used to query and manipulate DB |
