The Worlds of Database Systems Flashcards
DBMS
Database Management System
database
A collection of data that is managed by a DBMS.
schema
logical structure of data
relations
data organized as a table
SQL stands for?
Structure Query Language
XML stands for?
eXtensible Modeling Language
What is information integration?
Joining the information of many related databases into a whole.
Data Warehouse
Where information from many legacy databases is copied periodically, with the appropriate translation to a central database.
DML stands for?
Data Manipulation Language
DDL stands for?
Data definition language
What does the execution engine do?
The execution engine issues a sequence of requests for small pieces of data, typically records or tuples of a relation, to a resource manager that knows about data files (holding relations), the format and size of records in those files, and index files, which help find elements of data files quickly.
Overview of Query Processing
Using DML, interacts with DBMS. Doesn’t affect the schema of database but may change content.
Database management system components
What does buffer manager do?
Task is to bring approciate portions of data from secondary storage (disk) where it’s kept permanantly, to the main-memeory buffers.
Usually the page or “disk block” is the unit of transfer between buffers and disk.
Partition the available memory into buffers.
What is a transaction?
Way that queries and DML are grouped.
A transaction is a unit that must be executed atomically and in isolation from one another.
Any query or modificiation action can be a transaction by itself.
Must be durable.
What is durability?
The effect of any completed transaction must be preserved even if the system fails in some way right after completion of the transaction.
Two major parts of transaction processor?
- concurrency-control manager
* responsible for assuring atomacity and isolation of transactions* - logging and recovery manager
* responsability to preserve durability of transactions*
What does storage manager do?
Job is to control the placement of data on desk and it’s movement between disk and main memory.
Keeps track of the location of files on the disk and obtains the block or blocks containing a file on request from the buffer manager.
Components of data
- Data: contents of data itself
- Metadata: the database schema that describes structure of and constraints on database
- log records: info about recent changes of the database, supporting durability of the database
- statistics: info gathered and stored by DBMS
- indexes: data structures that support effecient access to data
ACID Properties of Transaction
‘A’ - “atomicity” – the all-or-nothing execution of transactions
‘C’ “Consistency” - all databases have consistency contraints, or expectations about relationships among data elements. Transactions are expected to preserve the consistency of the database.
‘I’ - “isolation” – the fact that each transaction must appear to be executed as if no other transaction is executing at the same time
‘D’ “durability” - the condition that the effect on the database of a transaction must never be lost, once the tranaction is completed
