Flashcards
Database
Cards in this deck (19)
- 1Drawbacks of file based databases?-Data redundancy
-Data inconsistency
-Data inconsistency - when the system's applications find it difficult to make updates/retrievals of data from multiple files
-Data integrity - it is difficult to alter system applications to implement new constraints, and the application programs require that the input/stored data to meet certain consistency criterias
-Data security- there are issues with accessing level privileges as well as implementing these constraints can be difficult
-Management of concurrency access - on File based systems, files are locked when a user is using it - 2How do RDBMS attempt to correct file based systems' weaknesses-Unitary storage in one software
-Reduced data inconsistency due to data minimisation
-Links can be used to refer to certain tables instead of repeating that data
-Reduced data duplications -> reduced quantity of data stored -> faster database access speed
-Concurrency management () - 3What is a logical schema and what is it intended for?A diagrammatic illustration of the structure of a database's model, showing how items such as tables, described accordingly to the database MS' specifications,
- 4How do data dictionaries in DBMS help address data management issues found in file based systems?Data dictionaries contains:
-detailed description of each piece of data
-relationships between data
-Access levels
-Rules for Validations
-Protocols for recovering data
-A map to distinguish between logics and physics - intended for storing
-A log of transactions for monitoring - 5What are developer Interfaces and Query processors and why are they used?Developer Interface: Allows graphical manipulation of database MS' features so it is more convenient for non-developers
Query Processor: handles high level language queries by compiling or interpreting. It parses (syntactically analyse), optimises and validates - 6What is referential integrity, secondary key and indexing?Prevention of entrance of inconsistent data
Secondary key: candidate keys not chosen to be PKs
Indexing: the duplication of various columns of data, can be low level disk block addressing or complete duplications, that allows searches, lookups and queries to be performed more quickly. - 7Criterias for 1NF, 2NF and 3NF?1NF: data atomicity, no repeated group of attributes
2NF: 1NF and no partial dependency
3NF: 2NF and no non-key dependency - 8What's the difference between Data Definition Language (DDL) and Data Manipulation Language (DML).DDL: used to define the overall database structure (creation, modification), using commands like ALTER, CREATE
DML: Used for data maintenance, with commands like SELECT - 9Create database syntax?CREATE DATABASE
- 10Create table syntax?CREATE TABLE (
;
...
PRIMARY KEY ()) - 11Changing table definition syntax?ALTER TABLE
ADD
ALTER TABLE
DROP COLUMN
ALTER TABLE
ALTER COLUMN - 12Add a primary key after table definition?ALTER TABLE
ADD PRIMARY KEY ()
For non-null constraint addition of pk where pk is previously null:
ALTER TABLE
ADD CONSTRAINT PRIMARY KEY (,) - 13Group by functions?Are functions that group the results by a column
GROUP BY (column1,column2,...) - 14Syntax for inner join?Selects all fields from both tables as long as there is one field that's the same on both table
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column1=table2.column2; - 15what do the fields after the SELECT clause represent?fields that will be shown in the result.
- 16INSERT INTO syntaxINSERT INTO tablename (column1,column2,column3,...)
VALUES (value1,value2,value3,...); - 17DELETE FROM syntax?DELETE FROM table_name
WHERE some_column=criteria; - 18UPDATE syntax?UPDATE table_name
SET column1=value1,column2=value2,...
WHERE some_column=criteria; - 19How do DBMS avoid data clashesRecord locks - locking a record as soon as it is modified, it can only be further modified by the same/different user if acknowledged by the first user that that data needs editing
-Serialisation - scheduling transactions (e.g. reading or writing) of data in a serial order
-Timestamps - each transaction has a timestamp that indicates when that record was last transacted, and is used by the DBMS to determine whether or not the data should be transacted
Commitment Ordering - looks at the priority and/or the impact of a transaction on a database and makes a decision on when to permit that transaction
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- Advanced Level (A- Level) Computer Science (Databases) Flashcards on Database, created by TS P on 01/01/2016.
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- TS P
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