ODBC
Open DataBase Connectivity
a standard database access method developed by
Microsoft
to access data from any application regardless of
which database management system (DBMS) is
handling the data.
ODBC middle layer- between an application and the
DBMS.
Translates the application's data queries into
commands that the DBMS understands.
Both the application and the DBMS must be ODBCcompliant –
the application must be capable of issuing ODBC
commands and the DBMS must be capable of
responding to them.
Central role for SQL
Driver
In addition to the ODBC software, a separate
module or driver is needed for each database to
be accessed.
Each database management system needs a
specific ODBC driver.
A driver is a program that interacts with a
particular device or special kind of software
e.g DBMS.
The driver contains the special knowledge of
the device or special software interface that
programs using the driver do not.
A driver is often packaged as a dynamic link
library (DLL, EXE or VXD) file.
-a small program, which can be called by a
program and executed when needed
ODBC is based on SQL Call-Level Interface
standard.
It allows programs to use SQL requests that
will access databases without having to
know the proprietary interfaces to the
databases.
ODBC handles the SQL request and
converts it into a request the individual
database system understands.
In the distributed object architecture,
Common Object Request Broker
Architecture (CORBA), the Persistent Object
Service (POS) is a superset of both the CallLevel Interface and ODBC.
Java Database Connectivity (JDBC), used
by Java to reach ODBC-accessible
databases.
The ODBC architecture has four components:
· Application. Performs processing and calls
ODBC functions to submit SQL statements and
retrieve results.
· Driver Manager. Loads and unloads drivers
on behalf of an application. Processes ODBC
function calls or passes them to a driver.
· Driver. Processes ODBC function calls,
submits SQL requests to a specific data source,
and returns results to the application. If
necessary, the driver modifies an application's
request so that the request conforms to syntax
supported by the associated DBMS.
· Data source. Consists of the data the user
wants to access and its associated operating
system, DBMS, and network platform (if any)
used to access the DBMS.
ODBC Architecture
Multiple drivers and data sources can exist, which
allows the application to simultaneously
access data from more than one data source.
The ODBC Application Program Interface is used
in two places:
1. between the application and the Driver
Manager,
2. and between the Driver Manager and each
driver.
The interface between a Driver Manager and
drivers is sometimes referred to as the service
provider interface, or SPI.
For ODBC, the application programming interface
(API) and the service provider interface (SPI)
are the same;
OLE DB
OLE DB and ODBC are Application Program
Interfaces that provide access to a range of
data sources.
e.g. enables a single Visualbasic program to
use data from many different databases,
maybe from different suppliers.
Microsoft designed ODBC to access SQL
data and OLE DB to access any type of data.
OLE DB has evolved from ODBC.
The difference is in the surrounding context
and in the generalization of a few main
terms;
Commonly used terms and what they mean in
ODBC and OLE DB.
Data source
ODBC-A relational DBMS
OLE DB-A module that wraps a data
store and exposes its content as a
set of rows and columns
Table
ODBC- A table in a relational
database
OLE DB- An aggregation of related
rows and homogeneous columns
Result set
A chunk of client memory that
holds a set of records
An independent and stand-alone
module that exposes a set of
records
Command
A SQL command interpreted by the
connected DBMS
A text string that the data
source can understand
OLE DB accesses all types of information—
relational and non-relational, flat and hierarchical,
persistent and volatile, based on SQL or on any
other query language.
Components, called data providers, ‘wrap’ (or
encapsulate) a data store.
This makes the data store a kind of ‘black box’.
Programs that use the data stores do not need to
know the internal workings of the data store.
They only need to know the detail of the interface
to the data store-this is standardised through OLE
DB.
The application that accesses the data is called a
data consumer e.g. Access 2000, Visual Basic
program
The program that enables native access to the
data is called a database provider e.g. Microsoft
OLE DB Provider for SQL Server or Microsoft Jet
4.0 OLE DB Provider .
This will be database specific I.e. there will need
to be a different data provider for every database.
A data link is the connection information that a
data consumer uses to access a data source
through the OLE DB provider of that data
source.
Consumer e.g.
VB program
Link
Provider e.g. Oracle,
SQL Server
Example Dialogs that create Data Links
Data Link file
Typically connect to an OLE DB provider from
Microsoft Access using the Data Link
Properties dialog box,
Can also define connection information for an
OLE DB provider in a Microsoft Data Link file
(.udl)
Microsoft Windows Explorer capable of creating
the file
(choose Microsoft Data Link from the New
menu, create a Microsoft Data Link file, select
the file name, right-click on the file name, and
then choose Properties).
e.g. file content- a connection string
Provider=SQLOLEDB.1;
Persist Security Info=False;
User ID=u878878;
Initial Catalog=car_hireSQL;
Data Source=scm-database
When connected to a data provider, a client
application (data consumer) always receives a
set of records, whether the data provider
manages tables from a relational database
management system (RDBMS), a directory
listing, a text file or whatever.
The data provider is responsible for retrieving
the data from the physical source and
formatting it.
The data can reside on a persistent medium
(disk files or databases), be kept in memory, or
span various machines and platforms.
It can be relational or hierarchical, structured or
flat, written in a standard or a proprietary
format, and accessible or inaccessible through
ODBC.
In addition, the result set (called a rowset or a
recordset) that OLE DB returns isn't a simple
stream of bytes copied into the client application's
memory, as with ODBC.
It's a stream of data that a standardised module,
with a separate programming interface, holds.
In other words, the data returned is not simply
data. It is data plus the means of manipulating
the data –an object.
The object is called a RecordSet.
Such an object gives you several facilities for
manipulating the recordset—sorting, filtering, and
scrolling—and it enables concurrent access to the
same data from multiple clients.
You can set up the data rows to work even when
they're disconnected from the data source.
OLE DB is a set of COM-based interfaces that
expose data from a variety of sources.
OLE DB interfaces provide applications with
uniform access to data stored in diverse
information sources, or data stores.
DSN
Data Source Name.
A Data Source Name provides connectivity to
a database through an ODBC driver.
The DSN contains
•database name
•Directory
•database driver
•UserID
•password,
•and other information.
The DSN can be used by an application to call
information from the database.
DSN is often used by Active Server Pages and
Visual Basic programs when a database
operation is necessary
The DSN is a connection made by the ODBC
server to a specified database.
This connection is assigned a name which can
be called by ASP (Active Server Pages), or
other programming/scripting languages to
manipulate the database.
Acts as a Data Link.
ASP is the consumer
DSN is the link
Database is the provider.
In the following the term Data Source is the
same as Data Link.
DSN vs DNS
Important not to confuse DSN and DNS
A Domain Name Server (DNS) is part of the
distributed Internet directory service.
A DNS is used to translate between domain
names and IP addresses
Most Internet services rely on a DNS to work
If the DNS fails, web sites cannot be located
and email delivery stalls.
Types of DSN
Three types of DSNs:
(1) System DSN (machine data source) -- can
be used by anyone who has access to the
machine and services, such as Microsoft
Windows NT services. DSN info is stored in
the registry.
(2) User DSN (machine data source) -- created
for a specific user. Also stored in the
registry.
(3) File DSN -- DSN info is stored in a text file
with .DSN extension
Machine Data Sources
Machine data sources only useable on the
computer they are defined on
Machine data sources store connection
information in the Windows Registry on a specific
computer with a user-defined name.
A machine data source provides added security,
Cannot be copied by a remote user to another
computer.
File Data Sources
File data sources store connection information in a
text file
More flexible to use than machine data sources.
A file data source can be copied to any computer
with the correct ODBC driver
The file data source can be
•placed on a single server,
•shared between many computers on the
network,
and the connection information easily maintained
in one location.
e.g
[ODBC]
DRIVER=SQL Server
SERVER=scm-database(local)
WSID=I5X3L2
DATABASE=bsc2
DSN-less connection
Instead of using a DSN to connect to a database,
the developer specifies the necessary information
in the application.
With a DSN-less connection the developer is free
to use connection standards other than ODBC,
such as OLE DB.
ODBC Data Source Administrator
The ODBC Data Source Administrator used to add
and configure data sources
The ODBC Administrator updates data source
connection information.
As data sources added the ODBC Administrator
updates the registry information.
Summary
•Application programs can be written and
configured so that they can access any
source of data (database, file, data stream,
directory…..etc) i.e. are physically
independent from data sources.
•Microsoft standard to achieve this is OLE
DB.
•Other suppliers use system software
(middleware) with a similar architecture e.g.
OMG/CORBA.
•Programs connect to data sources and
receive data in the form of objects (record
sets)
•Connections are established by defining
Data Links.