Accessing Databases from Applications

 

1.  What are the functions of ODBC?

      ODBC refers to Open Database Connectivity, and some of its functions are:

·        Enables applications to communicate with a variety of databases, such as Oracle and SQL Server

·        Facilitates SQL grammar conversion

·        Enables a single application to use different drivers

·        Enables applications to interact with different types of database using database features that exceed the features supported by a particular RDBMS

·        Allows the use of enhanced RDBMS features

·        Enables applications to achieve a three-layered architecture

2.  What are the components in the ODBC and what the interaction between them?

• Application
• Driver
• Driver manager
• Data source

3.  What is the difference between the types of DSNs?

DSN refers to Data Source Name. There are three types of data sources:

• User DSN – an ODBC User data source stores information about how to connect to the indicated data provider. A User data source is only visible to you, and can only be used on the current machine.
• System DSN – an ODBC System data source stores information about how to connect to the indicated data provider. A System data source is visible to all users on same machine, including NT services
• File DSN – an ODBC File data source allows you to connect to a data provider. Only users who have the same drivers installed can share file DSNs.

4.  What is the UDA strategy?

      UDA removes the dependency on different tools and languages for data access. It is based on open standards. As a result, a number of third-party developers support this standard. To implement UDA, Microsoft provides Microsoft Data Access Components (MDAC). MDAC is a combined name for technologies such as ODBC, Object Linking and Embedding Database (OLEDB), and ADO. ODBC is developed to access relational databases. However, OLEDB, which is built along the same lines as ODBC, is created to access relational as well as non-relational data sources, such as SQL Server 2000 and FoxPro.

      More information at:

      http://www.topxml.com/conference/wrox/1999_dc/text/dinouda.asp   

      http://www.topxml.com/conference/wrox/1999_dc/Powerpoints/dinouda.pps

5.  What is the role of ADO in the OLEDB model?

      ADO (ActiveX Data Objects) represents an object mode that is interfaced with OLEDB providers. The ADO object model uses object-oriented programming techniques to communicate with the underlying data source. ADO is independent of any language or OLEDB provider. Any language that supports COM interfaces can use ADO. ADO creates a layer between the applications and the OLEDB provider. This layer is easy to use. In addition to retrieving and manipulating data, ADO has the following functionality:

• Accessing data from e-mail systems
• Extracting data from data sources in XML
• Allowing changes to the data in databases
• Executing stored procedures
• Creating data structures called recordsets to display and manipulate data
• Performing transactional database operations
• Creating data-aware interfaces
• Creating disconnected recordsets.

6.  What are the objects in the ADO object model?

     The ADO object model consists of nine objects and four collections. Different objects are combined to form collections. The collections are available for different ADO objects. The nine objects are:

·        Connection

·        Error

·        Command

·        Recordset

·        Record

·        Parameter

·        Field

·        Property

·        Stream

The four collections are:

• Fields
• Properties
• Parameters
• Errors

7.  What are the steps to access a database from an application by using ADO?

      Applications are programs that call the ODBC API (Open Database Connectivity Application Programming Interface) to communicate with the RDBMS. An application communicates with database by passing SQL statements to the RDBMS. To do this, the application first connects to the database and then passes the SQL statements. To establish a connection with an SQL database and execute statements against it, the following steps are required:

• Set up a reference to the ADO connection object to create a new instance of the ADO connection object
• Define the connection string to be used when opening the connection object. The connection string can be defined in two ways, with a DSN:

                  ConnectionString = “DSN + Projects;

                  User ID = sa;

                  Password = “”;

• and without a DSN

                  ConnectionString = “Provider=SQLOLEDB.1;

                  Persist Security Info=False;

                  User ID=sa;

                  Initial Catalog=Projects;

                  Data Source= (local)”

• Open the connection object by using the Open method of the connection object
• Check if the connection has successfully opened by using the State property of the connecrtion object
• When the connection object is open and available, execute the SQL statements on the Project database
• Depending upon the requirements, create a recordset object and execute it by using the Open method of the recordset object. Multiple recordsets can be opened using the same connection object
• After the transaction with the database is over, close the recordset object. In addition, close the connection object by using the Close method of the connection object.

8.  Why is XML ideal for data interchange?

     The use of XML (Extensible Markup Language) helps to simplify the application architecture. It also leads to language independence. XML is compatible with low-level protocols such as HTTP because it can be used along with HTML to display data on the Web pages in a structured manner. This helps to place different objects of separate layers on different servers. Web clients, such as browsers, use HTTP to send request to Web servers. Based on the user requests, Web servers send the requested HTML page back to the user. This communication takes place over HTTP.

9.  What are the advantages of using XML?

• Providing extensible tags for defining application-specific data structures
• Enabling the creation of platform-independent applications
• Helping faster document searches over the Internet
• Helping to educe Internet traffic
• Uploaded the most recently updated version of the document on the Internet
• Helping to deal with data and its appearance on the Web, so that the same information can be displayed in different formats, if required.