lec 1 Flashcards
Record
- identifiable collection of data elements
- some collection of attributes that describe some entity or event
- basic unit of storage that a user recognizes
file
named collection of occurences of logical records which may be of more than one logical record type; a set of application record values pertaining to one or more record formats
Field
smallest meaningful unit of information of interest
Sequential access
method of using tape storage
record key
data element chosen to record the data set is called the key
Direct Access
The first access method designed to make use of the ability to quickly go to any location on a disk
- Records stored in fixed locations based on the values of key fields that can be directly mapped to a physical location on a disk
(records are accessed in their original location)
Indexed sequential access
optimized access speed with storage space utilization as a major improvement over direct access
- Records stored in FCFS manner are quickly accessed using an inex of pointers from record keys to the locations of the records (index resorted each time it is updated)
(records are accessed in their original location)
file based system
a collection of application programs that perform services for the end users, such as the production of reports
File based approach
typically bottom up
to meet the needs of a small group of users
often on local departmental systems
Disadvantages of file based approach
- seperation and isolation of data(data sharability)
- duplication of data (data inconsistency)
- data dependence (data structures highly independent)(data evolvability)
- incompatible file formats (programs and languages) (data sharability)
- no standard for queries(you have to develop your own
database
a shared collection of logically related data, designed to meet the information needs of an organization
Database approach advantages
Data integrity - ensuring the correctness, protection and security of the data
data sharability - ensures data can be shared between applications and users on a need to know basis
data availability - data can be accessed when and where it’s needed
data evolvability - ensures database can be modified to meet changing needs
Avoids redundency - where multiple copies of data are collected and used independently
disadvantages of database approach
- complexity - highly trained staff needed, organizational infrastructure to handle costs, evolutionary planning, hardware and software support
- large DBMS have high cost and are closed source
- cost of conversion
- Performance - additions may slow down applications
- high impact of failure - department or organization
To create a successful database
-
it takes understanding the data and needs of users
Ansi-sparc architecture
To seperate each users view of the database, from the way the database is physically represented
- database administrator - controls physical internal and conceptual structures
Ansi-sparc arcitecture
- external level - user’s view of the database, that part of the database that is relevant to each user
- conceptual level - community view of the database, what data is stored in the database and the relationships(complete set of data)
- internal level - describes data stored on computer, physical representation on computer (IT only)
- physical organization of data - managed by opereating system under DBMS
schema
description of database (not in physical organization of data level )
mapping
consistent correspondence between mapping at different levels
instance
the data in a database at a particular instance in time
independence
- immunity of one level of a database to changes at a lower level
data definition language
language that allows the dba or user to describe and name entities, attributes and any relationships required for the application together with any associated integrity and security constraints
data manipulation language
language that provides a set of operations to support the basic data manipulation operations on the data held in the database
procedural dml
a language that allows the user to tell the system what data is needed and exactly how to retrieve the data
non-procedural dml
a language the allows the user to state what data is needed rather than how it is to be retrieved
fourth generation languages
non-procedural languages that typically include a number of tools to help quickly develop applications
- can limit the developers freedom
basic data processing functionality
- data storage retrieval and update (DML)
- user-accessible catalog (DDL)
Business integrity supporting functionality
transaction support, concurrency control services, recovery services, authorization services, support for data communication
transaction support
to ensure all or no parts of a transaction are processed
concurrency control services
to ensure updates are completed before begin updated
recovery services
to repair damages to db
authorization services
to protect the database from unauthorized accessing
support for data communication
support decentralized access by workers and clients
DB administration functionality
integrity services
services to promote data independence
utility services
integrity services
to assist in evolving the database
utility services
allow tuning of the data
Client server architecture
server program
manages database, maintains system catalog, accepts and processes database requests from client, checks authorization and complaints, provides concurrency and recovery, performs query/update processing and transmits response to clients
client server architecture
manages the user interface, processes the application logic, accepts and checks syntax of user input, generates database requests and transmits to server, passes response back to user
electronic data exchange
automated exchange of any predefined and structured data for business purposes among information systems of two or more parties
Business operational view
involves standardized data elements
used by user communities
to produce open-edi scenarios
registered by a registration authority
functional service view
involves standardization communications and db technologies
used by it designers and it implementers
combined with oped-eid scenarios
to enable the execution of open-edi transactions
open-edi scenario
formal specification of a class of business transactions having the same goal
Business transaction
“a predefined set of activities and/or processes of parties which is initiated by a party to accomplish an explicitly shared business goal and terminated upon recognition of one of the agreed conclusions by all parties although some of the recognition may be implicit.”
