Data Managment

Frage	Antworten
Hard Disk Drive (Magnetic Disk)	- data storage device used for storing and retrieving digital information - consists of one or more rigid ("hard") rapidly rotating disks with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces Image: 9c8433dc-361b-4a27-8341-7153608ab2d7.JPG (image/JPG)
Hard Disk Structure	- Block, cylinder and sector structure - Block contains 512 bytes
Seek Time	Average Time to change from a random track to another track (3-12 msec)
Latency Time	Time to mechanical change track, depends on rotation speed, half period of rotation (5-2 msec)
RAID (Redundant array of independent disks)	- storage technology that combines multiple disks drive components into logical unit for the purpose of data redundancy and performance improvements - Data distributed across the drives in one or several ways, referred to as RAID levels
RAID 0 (block level striping)	- no redundancies - improved performance and additional storage - no fault tolerance - any drive failure destroys whole array
RAID 1 (mirroring without parity or striping)	- data written identically to two drives, producing a "mirrored set" - read request is serviced by either of the drives
RAID 5 (block level striping with distributed parity)	- distributes parity along with the data - not destroyed by single drive failure - any subsequent reads can be calculated from the distributed parity, in case of failure - at least 3 disks
Flash Memory	- also Computer memory - particular type of "electronically erasable programmable read-online memory" (EEPROM) - often used in portable electronics
Flash Memory - Speed Advantage	- differs from regular EEPROM because it can delete data in entire blocks - preferable technology for applications that require constant, large data updates
Flash Memory - General Advantages	- non volatile, solid state - no moving parts - silent - smaller than HDD - highly portable - much faster access time
File System	- used to control how information is stored and retrieved - without it -> one large body of information where we don't know the end and the beginning - part of operating system
Operating System	- collection of software - manages computer hardware resources - provides common service for computer programs
Cloud Computing (CC)	- synonym for distributed computing over a network - ability to run programs on many computers at the same time
Cloud Clients	Applications work like with every other operating system Customized operation system is accessible from everywhere in the internet
Software as a Service (SaaS)	users are provided access to application software and databases (CRM, Email, communication, games, virtual desktop)
Platform as a Service (PaaS)	- Cloud providers deliver a computing platform - typically including operation system, database and web server
Infrastructure as a Serice (IaaS)	- providers of IaaS offer computer-, physical or virtual machines and other resources
Properties of CC	- On demand Self-Service - Broad Network Access - Ressource Pooling - Rapid elasticity - Measured service
Database Application Examples - Traditional Database Application	Store textual or numeric information
Database Application Examples - Multimedia Databases	Store Images, audio clips Video streaming digitally
Database Application Examples - Geographical information systems (GIS)	Store and analyse maps, weather data and satellite images
Database Application Examples - Data Warehouses and analytical processing (OLAP) systems	Extract and analyse useful business information from very large databases Support decision making
Database Application Examples - Real-Time and active database technology	Control industrial and manufacturing processes
Database Application Examples - Large Commercial Database	Amazon.com
Database (DB)	organized collection of Data
Database management systems	specially designed applications interacting with the user, other applications and the database itself to capture and analyse data software designed to allow the definitions, creation, querying and update and administration of databases well know DBMS: MySQL, SQLite, Oracle, SAP standards like "SQL" allow applications to work with more than one DB enables users to create and maintain a DB
Query	Causes some data to be retrieved
Transaction	May cause some data to be read and some data to be written into the database
Protection	System protection Security protection
Maintain a database system	Allow the system to evolve as requirements change over time
Simplified Database System environment	Image: b8dd2787-c277-4e46-93df-8e6573ff21db.JPG (image/JPG)
Phases for designing a database	1. Requirements specification and analysis 2. Conceptual design 3. Logical Design 4. Physical desingn
Traditional File processsing	Each user defines and implements the files needed for a specific software application
Database Approach	Single repository maintains data that is defined once and then accessed by various users
Main characteristics of Database Approach	self describing nature of database system Insulation between programs, data and data abstraction Support of multiple views of the data Sharing of data and multiuser transaction processing
Defining a database	Specify the data types, structures and constraints of the data to be stored
Meta-data	Describes structure of the database
Manipulating a database	Query and update the database
Application program	Accesses database by sending queries to DBMS
Database catalog used by ... :	DBMS Software Database users who need information
Program-data independence	Structure of data files is stored in DBMS catalog separately from access programs
Program-operation independence	- Operation specified in two parts * Interface includes operation name and data types of its arguments * Implementation can be changed without affecting the interface
Data Abstraction	Allows program-data independent and program-operation independence
Sharing of data and multiuser Transaction Processing	Allow multiple users to access the database at the same time
Concurrency Control Software	Ensure that several users trying to update the same data do so in a controlled manner Result of the updates is correct
Isolation property	Each transaction appears to execute in isolation from other transactions
Atomicity property	Either all the database operations in a transaction are executed or none are
Database administrators (DBA) are responsible for:	Authorizing access to the database Coordinating and monitoring its use Acquiring software and hardware resources
Database designers are responsible for:	Identifying the date to be stored Chosing appropriate structures to represent and store this data
End users	People whose jobs will require access to the database ( Casual end users) (Naive or parametric end users) (Sophisticated end users) (Standalone users)
System analysts	Determine requirements of end users
Application programmers	Implement these specification as programs
DBMS system designers and implementers	Design and implement the DBMS modules and interfaces as a software package
Tool developers	Design and implement tools
Operation and maintenance personnel	Responsible for running and maintenance of hardware and software environment for database system
Controlling Redundancy	Data Normalization De-normalization
Backup and recovery subsystem	responsible for recovery
Enforcing integrity contraints - Referential integrity constraint	Every section must be related to a course record
Enforcing integrity contraints - Key or uniqueness constraint	Every course record must have a unique value for Course_number
Data abstraction	Suppression of details of data organization and storage Highlighting of the essential features for an improved understanding of data
Data Model	Collection of concepts that describe the structure of a databases Provides means to achieve data abstraction
High level / conceptual data models	Close to the way many users perceive data
Low Level or physical data models	Describe the details of how data is stored on computer storage media
Representational data models	Specify retrievals and updates on the databse
Entity	Represents a real-world object or concept
Attribute	Represents some property of interest Further describes an entity
Relationship among two or more entities	Represents an association among the entities "Entity-Relationship model"
Relational data model	Used most frequently in traditional commercial DBMSs Represents data as a collection of relations
Physical Data Model	Describe how data is stored as files in the computer
Access Path	Structure that makes the search for particular database records efficient
Index	Example of an access path Allows direct access to data using an index term or a keyword
Database schema	Description of a database
Schema diagram	Displays selected aspects of a schema
Database Construct	Each object in the schema
Database state / Snapshot	Data in database at a particular moment in time
Three Schema architecture	Internal level Describes physical storage structure of the datbase ________________________________________________ Conceptional level Describes structure of the whole database for a community of users ________________________________________________ External / View Level Describes part fo the database that a particular user group is interested in
DBMS Languages	Data Definition Language (DDL) Storage definition language (SDL) View definition language (VDL) Data manipulation language (DML) High level or nonprocedural DML Low level or procedural DML
Computer-aided software engineering (CASE)	application of a set of tools and methods to software system desired result: high quality, defect free and maintainable software products
Server-types	File Server Printer Server Web / Email servers
Client machines	Provide user with: - Appropriate interfaces to utilize these servers - Local processing power to run local applications
Server	System containing both hardware and software Provides services to the client machines (file access, printing, archiving, database access)
JDBC	Allows Java client programs to access one more DBMS through Stnadard interface
ODBC (Open Database Connectivity)	Provides application programming interface (API) Allows client-side programs to call the DBMS (Client and Server machines
Relation Data Model - Row	Represents a collection of related data values Tuple
Relation data model - Attribute	Meaning of the values in each row
Relation Dartabase Model - Cardinality	Total number of values in domain
Relation Database Model - Constraint	Restrictions on the actual values in a database state Derived from the rules in the mini world that the database represents
Relation Database Model - Superkey	No two tuples can have the same combination of values for all the attributes No two distinct tuples in any state r of R can have the same value for SK
Relation Database Model - Key	Superkey of R Removing any attribute A from K leaves a set of attributes K that is not a superkey of R any more
Relation Database Model -Minimal superkey	Cannot remove any attributes and still have uniqueness constraint in above condition hold
Relation Database Model - Candidate Key	Relation schema may have more than one key
Relation Database Model - Primary key	Desginated among candidate keys Underline attribute
Relation Database Model - Entity integrity constraint	No primary key value can be NULL
Operations of the relational model	Operations of the relational model can be categorized into retrievals and updates
Basic operations that change states of relations	Insert Delete Update
INSERT Operation	Provides a list of attribute values for a new tuple t that is to be inserted into a Relation R Can violate any of the four types of constraints If insertion violates one or more constraints the insertion is rejected
SQL language	major reasons for the commercial success of relational databases
SQL	Structured Query Language Statements for data definitions, queries and updates
CREATE statement	Main SQL command for data definition
CREATE SCHEMA statement

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	Erstellt von kai.kullwitz vor fast 9 Jahre