Download Paper on ODBC

Ryan Stroup
Web Programming 11:00
ODBC
Intro
ODBC stands for Open Database Connectivity. ODBC evolved over many years
in the late 1980’s and early 1990’s. ODBC was created through the contributions of
many, many groups, as you will read later on in this paper. ODBC is most useful for
accessing relational data and not well suited for accessing other types of data. ODBC has
been refined over and over and still there are many complaints about it.
Background
The first version of ODBC was created by the SQL Access Group (SAG) in 1988.
The SQL Access group was comprised of 44 database vendors whose goal was to create a
unified standard for remote database access. The SAG was focused on two main goals.
One was to create a standard that allows any database client to talk to any database server
by using common message formats and protocols. The second was an SQL Call Level
Interface (CLI) that defines a common Applications Programming Interface (API) set for
multi-vendor databases [9].
The SQL Access Group eventually developed SAG CLI that allowed a user to
connect to a database through a local driver, prepare SQL requests, execute the requests,
retrieve the results, terminate a statement, and terminate a connection. The SAG CLI
only supported dynamic SQL [9].
In August 1992, Microsoft released an ODBC Windows API, which was an
extended version of the SAG CLI [9]. ODBC uses standard query language (SQL) as the
standard for accessing data. Microsoft’s ODBC included functions for accessing the
database catalog and for controlling and determining the capabilities of ODBC drivers
and their data sources [8]. There have been numerous other ODBC versions released
over the years and at present the future of ODBC is uncertain [9].
ODBC was developed for corporate use. Companies needed a way to
communicate between applications and SQL databases so ODBC was a huge
breakthrough for companies that relied on relational databases. I believe ODBC started
as something much more simpler than it is today. With each new release of ODBC, each
version became more sophisticated and complex.
Overview of ODBC
The first release of ODBC was ODBC 1.0. This was very slow and contained
many bugs. ODBC 1.0 was limited to the Windows platform and lacked the
documentation and code examples required to help educate developers. In 1994
Microsoft released ODBC 2.0 SDK. This new release fixed many of the bugs with the
previous device manager [9].
ODBC 3.0 SDK was released in 1996. Microsoft claimed this version offered
enhanced performance, extensibility, and alignment with open standards such as X/Open
and ISO [5]. This helps show that with each new ODBC version that is released, the
versions are becoming more and more sophisticated and user-friendly.
It is very interesting the way ODBC works. Once again the goal of ODBC is to
make it possible to access any data from any application, regardless of which database
management system (DBMS) is handling the data. First of all before anything else,
ODBC is very hard to program and implement [2]. The way ODBC works is by inserting
a middle layer, called the client driver, between an application and the DBMS. The
purpose of the database driver is to translate the applications data queries into commands
that the DBMS understands. For this to be successful, both the application and the
DBMS need to be ODBC compliant [6].
For an ODBC connection there are five parameters that will then need to be
defined. The five parameters are the specific ODBC driver needed, the back-end server
name to connect to, the database name to connect to, the user id to be granted access to
the database, and the password of the user id [2]. The ODBC interface was coded in the
C programming language. The typical ODBC architecture looks like the figure below
[4].
As you can see the architecture is composed of four different parts: database
application, driver manager, drivers, and the database. The database application calls
functions defined in the ODBC API to access a data source. The driver manager
implements the ODBC API and provides information to the application. Microsoft’s
driver manager is a dynamic link-library file named odbc32.dll [5]. With Unix, the
ODBC driver is a shared library [10]. The database contains all the data that an
application needs to access [10].
The client drivers are the key part in all of this. The client driver must manage
numerous details for everything to communicate together properly. Some details it must
manage are the differences in each server’s SQL implementation, the format which the
server requires for its requests and the format of the responses, the need to support the
server’s protocol, differences in the way that different servers encode data, naming and
location, and connection management between the client and server. The drivers are very
flexible and can incorporate the services of any client/server framework [1]. ODBC
drivers are usually obtained from database and front-end tool vendors [9].
Another characteristic of ODBC is that it contains three conformance levels. The
three levels are the Core, Level 1, and Level 2. I will look at these as they appeared in
ODBC 2.0. The Core level provided 23 base call that let a user connect to a database,
execute SQL statements, fetch results, commit and rollback transactions, handle
exceptions, and terminate the connection [9]. Some of the more common core functions
are SQLConnect(), SQLCancel(), SQLError(), SQLExecute(), and SQLFetch() [10].
Level 1 provided an addition 19 calls that allowed a user retrieve information
from a database catalog, fetch large objects, and deal with driver specific functions [9].
Some Level 1 functions are SQLColumns(), SQLGetData(), SQLTables(),
SQLPutData(), and SQLDriverConnect() [10].
Last, Level 2 provided another 19 calls that let a user retrieve data using cursors.
Also Level 2 supported forward and backward scrolling [9]. The applications determine
the conformance level when they call the driver [2]. A few Level 2 functions are
SQLDrivers(), SQLPrimaryKeys(), SQLProcedures(), SQLSetSCrollOptions(), and
SQLForeignKeys() [10].
Advantages and Disadvantages
There are many advantages and disadvantages about ODBC. Perhaps the biggest
advantage is that the ODBC API is available on all major platforms. ODBC has become
so accepted that some vendors have developed their DBMS native programming interface
based on ODBC. This vast acceptance of the standard was initially propelled by
Microsoft’s implementation of ODBC for their products [2]. Microsoft’s platforms also
include many enhancements that other platforms do not contain. Another big advantage
of ODBC is dynamic data binding. This allows the user or system administrator to easily
configure an application to use any ODBC compliant data source. Dynamic binding
allows the end-user to pick a data source and use it for all data applications without
having to worry about recompiling the application [7].
But like I mentioned ODBC has many drawbacks associated with it as well. The
largest drawback is that Microsoft controls the specification and it is constantly evolving.
Companies for the most part have to evolve with Microsoft, which is something they
obviously like to keep to a minimum. Along with this comes the price of Microsoft’s
ODBC. Microsoft has exercised control of ODBC by making companies pay for the
ODBC SDK [8].
Another big problem is the future of ODBC is uncertain. Microsoft has shown
commitment to OLE/DB. OLE/DB introduces a different programming standard as it
leans more to object-based rather than procedural. But Microsoft is promising continuing
support to ODBC as well as OLE/DB so this issue will have to wait to the future to be
resolved. The drivers for ODBC are also very complicated to build and maintain. The
current drivers have different conformance levels, which are not documented very well.
The ODBC layers present a lot of overhead and they are not known to be very fast [9].
Also ODBC does not specify the communication framework because it only
specifies the application protocol. Thus ODBC inherits the features of the underlying
framework. So reliability depends on how the server and the driver implement their
request-response protocol. The client performs much of the work to make up the
differences between the client and different server systems. This is an obstacle to scaling
and also causes servers to not be sufficiently standardized [1].
As a result of this each client maintains its own drivers, naming tables, and
macros, which could complicate management at larger sites. Developers even often
experience problems getting multiple ODBC drivers to work together on a single client
machine [1]. A few more issues with ODBC are its complexity of implementation and its
lack of a simple object model [3]. A quote by Richard Frankenstein shows the way a lot
of developers feel about ODBC
“Use native (direct) APIs whenever possible. Standard APIs like ODBC should
be considered as a last resort…not the first” [9].
From my personal use with ODBC, I have found that it is very simple to use. I
was able to start using it immediately without having to be taught much about it. I
believe this view is shared among most users of ODBC. The one disadvantage that was
clearly visible to me was that with a larger DBMS, ODBC could at some points be very
slow.
Summary
ODBC is extremely useful for company’s to manage their relational databases. It
is simple to learn and makes it easy to access and update data. But ODBC also has its
share of limitations. Overall I think ODBC was and is very important in today’s
technological society.
REFERENCES
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Professionals. New York: Addison-Wesley Publishing Company, 1995.
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Upper Saddle River, New Jersey: Pearson Education, Inc., 2002.
3. Jerke, Noel, et al. Visual Basic 5 Client/Server How To. Corte Madera, CA:
The Waite Group Press, 1997.
4. Lee, Wei-Meng. “The Evolution of Data-Access Technologies.” SQL Server
Magazine. Apr. 2002. 24 Oct. 2004. http://www.winnetmag.com/
SQLServer/Article/ArticleID/23988/23988.html
5. Microsoft Announces ODBC Version 3.0 SDK. 12 Nov. 1996. Microsoft Corp.
19 Oct. 2004. <http://www.microsoft.com/presspass/press/1996/nov96/
odbcskpr.asp>.
6. ODBC. 16 Aug. 2004. Webopedia. 18 Oct. 2004 <http://www.webopedia.com/
TERM/O/ODBC.html>.
7. ODBC and the unixODBC project. 20 Sep. 2004. 17 Oct. 2004.
< http://www.unixodbc.org/>.
8. Open Database Access and ODBC. 1998. FFE Software, Inc. 14 Oct. 2004.
<http://www.firstsql.com/ioodbc.htm>.
9. Orfali, Robert, Dan Harkey, and Jeri Edwards. The Essential Client/Server Survival
Guide. New York: John Wiley & Sons, Inc., 1996.
10. Visigenic DriverSet Reference Version 2.0. 1996. Visigenic Software, Inc.
26 Oct. 2004. <http://www.prolificmuse.com/About_Prolific_Muse/
Printed_Documentation/drivset.pdf>.