Presentation Middleware, Assignment 7.5

The assignment:

 

Establish an ODBC connection, which can be used for requests between a client application and the DBMS used at our institute.

Middleware, an overview

As you must know by now, there are several types of middleware:

Remote Data Access (RDA), which implements a RDA protocol for sending data manipulation language statements to an appropriate database server for processing and transporting the result back to the invoking process.
Remote procedure calls (RPCs). RPC is used in most network operating system services.
Message-oriented middleware (MOM). MOM can be used as a mechanism for storing and forwarding messages queuing.It can be used when client and server processes communicate asynchronously.
Object Request Brokers(ORBs). A standard implementation of the ORB standard is CORBA. ORB makes it possible to invoke a remote object by allowing a source object to send a message to that remote object.
Distributed transaction processing (DTP). This type of mechanism use execution semantics to interact between the client and the server.

 

Microsoft Open Database Connectivity (ODBC)

 

ODBC is an open, vendor-neutral and powerful interface that allows applications to seamlessly access over 50 different database systems through a common set of functions. With this powerful technology, developers don't need to learn multiple programming interfaces since they can use the universal set of interfaces provided by ODBC.

Microsoft's Open Database Connectivity (ODBC) interface allows applications, through database drivers, access to data in a variety of database management systems (DBMS). This allows users to evaluate their own database environment and add ODBC database drivers without the need for changes to the ODBC enabled application. MicroStation 95/MicroStation SE provides a database server written with the ODBC interface. The MicroStation server passes requests through an ODBC database driver to the underlying DBMS. MicroStation does NOT deliver the ODBC database driver(s). The user is responsible for purchasing ODBC database drivers for the DBMSs that need to be accessed. There are several companies that provide ODBC drivers. These were evaluated before development was started and the initial development and testing has been done with Intersolv and Microsoft.

Standards supported in Microsoft ODBC: ANSI SQL, ISO 9075, X/Open SQL CLI.

 

ANSI SQL [ISO 9075-3] ANSI SQL is a specification for SQL from ANSI. American National Standards Institute (ANSI)

ISO 9075-3 [SQL/CLI] ISO 9075-3 is a standard from ISO based on the SQL Access Group (SAG) specification for Call Level Interface (CLI).

In the picture below is showed how a connection is established using ODBC.

Here is a general description of the application, which is used by the school's helpdesk. They have a database with entries based on the users login names. In the database, problems with their history and solutions are stored. The database also contains user-specific data. The database is part of the school's Helpdesk application.

The helpdesk department has a Microsoft SQL Server running on a Windows NT computer. The database is accessed by clients. The client machines are using a program, which is running on Windows 95 machines. The client makes a connection to the SQL server using ODBC. The used Client is Support Magic by Magic Solutions.

According to Magic Solutions, the vendor of Support Magic, Support Magic is the industry's most popular user interface. It's a highly integrated system with an open API. A robust, low-cost support solution that can grow with a business. Whether the helpdesk supports 10 people or 1,000, Network Associates delivers everything you need for success. With standard SQL database support and a remarkably flexible interface, Magic Help Desk SupportMagic Edition lets the administrator control everything without programming. Designed for the small to mid-range internal helpdesk, Magic Help Desk packs the power and versatility of an open, fully customizable database into a low-maintenance, "out-of-the-box" support management solution.

It has the the following features:

• It provides comprehensive Help Desk Functionality
• Powerful Web User Interface
• Advanced Knowledge Management can be done
• Customization
• Multiple Group Support
• User-friendly Database Administration
• End-user Self-service

With SQL Server for Windows NT, Microsoft created a database engine that looked like SQL Server, walked like SQL Server and even quacked like SQL Server, but which wasn't an ordinary SQL server.

Microsoft rewrote SQL server to use native operating system services for threads, memory management, disk I/O, symmetric multiprocessing support, and even Windows NT's networking services. This was a complete break with the past.

Microsoft SQL server uses threads. Instead of simulating threads in the database kernel, as other servers did before, SQL Server used native Win32 operating system threads - meaning that those threads ran in protected memory spaces, preemptively scheduled by the Windows NT OS kernel. This is called the Symmetric Server Architecture, which is shown here...

In Microsoft SQL Server a user connection is given a distinct thread in the database kernel, but in Microsoft SQL Server on Windows NT, that thread is a Win32 operating system thread. It's bound by the restrictions of Windows NT's memory protection, thread scheduling, and hardware-access rules, but it also has all the features of a Win32 thread . out of the box support for multithreading, access to striped hardware devices, and memory protection for individual threads. With this architecture, a single corrupt thread no longer crashes the entire executable; instead, SQL Server can trap the offending thread and continue execution.

• SQL Server does not recognize some ANSI SQL data types such as number, numeric, decimal, integer, logical. The following data types ARE recognized: money, smallmoney, int, smallint, tinyint, char(n), varchar(n), text, datetime, smalldatetime, bit, timestamp, sysname, float, real, binary(n), varbinary(n), image.
• SQL Server treats NULLs in a non ANSI manner. While ANSI standards specify that a column by default can accept NULL values, in SQL Server you must specify a column as NULL in order for it to accept NULL values. The NOT NULL option on columns works as expected. This can lead to problems with active entity creation. If a column in the active entity table does not have a value, the active entity can not be inserted into a table unless the create table statement defined the no value column with the NULL option.
• The Intersolv ODBC SQL Server driver does not support SQL statement over 2400 characters at this time.
• SQL Server 4.2 is supported on MicroStation 95. A new ODBC server which provides SQL Server 6.5 support for MicroStation SE is available. To use the new ODBC server, users are required to upgrade their Microsoft ODBC drivers to version 3.51.

In the picture below can be seen what steps are taken to make a connection:

1. A client makes a request to the server.
2. The server verifies the client and processes and/or parses the request.
3. The server accesses the needed datasources.
4. Finally, the server returns the results to the client.

• Connection is made by using "Support Magic Helpdesk" by Magic Solutions.
• The client establishes an ODBC connection.
• In principle it would be possible to use another application, which also supports ODBC or even write your own client to access the SQL server.

1. What kind of Middleware is ODBC?
2. What kind of Helpdesk application is used by the school?
3. What happens if a thread gets corrupt?

• Microsoft SQL Server 6.5 Second Edition Solomon, Rankins, et al., ISBN 0-672-30956-4
• http://ourworld.compuserve.com/homepages/VBrant/
• http://www.microsoft.com/data/odbc/prodinfo.htm
• http://www.microsoft.com/sql/
• http://www.magichelpdesk.com/

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