Flashcards
Databases 2: Database schemas and design
Flashcards do conjunto (12)
- 1What are concurrency control protocols?-Protocols that prevent database accesses interfereing with each other
- 2What is the central notion in a DBMS and define itA transaction. An action/series of actoins carried out by a single user/program which reads/updates the database.
- 3What happens to the database's state during/after a transaction? What are the two outcomes of a transaction?During: DB may be in an inconsistent state
After: Database in consistent state, valid integrity/referential constraints
Outcomes:
committed - successful completion
rolled back - unsuccessful completion - 4What is concurrency control?Process of managing simultaneous operations on the DB without having them interfere with each other.
- 5What are the 3 characterisations of data?-Structured data
-Semi-structured data
-Unstructured data - 6What is a data model?Collection of intuitive concepts describing data, their relationships, and constrains.
Used as DDL is too low-level to describe data organisation in a simple, easily understandable way. - 7What is structured data and what does the DBMS do to check it?-Data represented in a strict format (schema)
-DBMS checks to ensure the data follows the structures, integrity & referential constraints specified in the schema - 8How does the relational data model work?Relations are tables (columns & rows)
Attributes are columns
Tuples are rows - 9What is the Entity-Relationship model?Graphical representation of database.
Concepts:
-Shows the important data objects (entities)
-Important properties of entities (attributes)
-Associations between entities (relationships)
-Has constraints on the entities, relationships, and attributes. - 10What is the 3-Level ANSI-SPARC architecture?External level (part of data that is relevant to each user - user's view of data)
Conceptual level (logical structure of data, as seen by DB administrator)
Internal level (physical representation of data in the DB). - 11What is data independence, logical data independence, physical data independence?- Upper levels in the DB schema are not affected by changes to the lower levels.
Logical data independence: external schemas remain the same if we change the logical structure of the data
Physical data independence: conceptual schema remains the same if we change the internal schema - 12What are the 3 main phases of database design?Conceptual design - construct a first, high-level model of the data: ER model, using requirements specification.
Logical design - construct relational data model of the data using the conceptual design
Physical design: describe the database implementation of the logical design. Aim is optimum performance.
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- FlashCards sobre Databases 2: Database schemas and design, criado por SEZ McKelvey em 06-04-2018.
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- SEZ McKelvey
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