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ASP DATA STORE & OBJECT MODEL Database Structure: Databases have a standard format of storing data; even if the database technology is different. Databases store information in tables & records. Each record is assigned a key; which is a unique identifier to differentiate records. Key values can be numeric or alphanumeric so long as they're unique within the key column.

Open Data-Base Connectivity (ODBC): ODBC is a standard for accessing data. It was designed to allow the programmer to use a common set of routines to access the data stored in databases, regardless of the type of database in which the data was stored. This meant that once the programmer was connected to the database using ODBC, they could manipulate the data without worrying exactly where the data was stored, or which type of database was storing it. It provided interface transparency – so the programmer could access an Oracle database in the same way that they accessed a SQL Server database. Data Store: Any persisted collection of information is a data store. Aside from all the databases in the world, there's a wealth of other data out there that's stored in other formats. It might be a spreadsheet containing your company finances, or a text file containing a report on the conference you visited last month, or an email system and its accompanying mail messages – but it's all data. We use the generic term data store to refer to a receptacle that contains data. Object Linking & Embedding Database (OLE-DB): OLE-DB is the next step in the evolution of the anonymous data store. As well as being more generic than ODBC, Microsoft has done a great deal of work to ensure that OLEDB is faster and easier to use than ODBC. Eventually it may well replace ODBC, although that won't be for a long time yet, if only for the reasons that you often have to rely on third parties writing new OLE-DB providers and then when they are available they are often more expensive than existing ODBC drivers. So, consequently, there's a lot more ODBC drivers out there still in use. The idea behind OLE-DB is very similar to the idea behind ODBC – but in fact it allows access to a much broader range of data stores. In fact, you'll notice that OLE-DB even supports database connections through ODBC – so that effectively your generic OLE-DB layer will allow you to connect to your legacy databases through your existing ODBC connections.

OLE-DB introduces the notion of data providers and data consumers. The relationship between a data provider and a data consumer is fairly obvious: a data provider is something that provides data, and the data consumer is something that uses that data. In reality, you might have several data providers – one for each different type of data store. ActiveX Data Object (ADO): ADO is a set of objects that allow programmers to program their data access logic from languages like Visual Basic as well as scripting languages. ADO is a higher-level model than OLE-DB, which means that it simplifies some of the complexities of programming with OLE-DB. Thus, ADO is much easier to use than OLE-DB. The ADO layer sits neatly between the application itself and the OLE-DB layer. ADO Object Model: The ADO Object Model has five main objects:  Connection  Command  Recordset  Record  Stream The following objects can be understood as follows: Connection Object: It acts as the link between the program and the data store. At one end, we have the Connection object and at the other end, we have one or other data store. In between, we have a connection that ties them together for as long as they need to communicate. The syntax to create a Connection object in ASP: Dim objConn Set objConn = Server.CreateObject("ADODB.Connection") In order to actually establish the connection we use the Open method of the objConn Connection object. The syntax for using the Open method is: objConn.Open ConnectionString, UserId, Password, Options The last four arguments are optional arguments – we don't have to specify any of them at the time we call the Open method. Once you have finished with a connection, you should Close it, in order to free associated system resources: objConn.Close Properties: ConnectionTimeout: Sets or returns the number of seconds to wait for a connection to open. Default is 15.

ConnectionString: Sets or returns the details used to create a connection to a data source. Provider: Sets or returns the provider name. Methods: Open: Opens a connection. Close: Closes a connection. Execute: Executes a query, statement, procedure or provider specific text. Command Object: It allows you to run commands against the data store. It is used to execute a single query against a database. The query can perform actions like creating, adding, and retrieving, deleting or updating records. The syntax to create a Command object in ASP: Dim objComm Set objComm = Server.CreateObject("ADODB.Command") In order to run a command, we use the Command object's Execute method. The Execute method has three parameters: objCommand.Execute RecordsAffected, Parameters, Options All three arguments are optional – if you omit any of them then the Execute method will adopt the default value for that parameter. Properties: ActiveConnection: Sets or returns a definition for a connection if the connection is closed, or the current Connection object if the connection is open. CommandText: Sets or returns a provider command. Methods: Execute: Executes the query, SQL statement or procedure in the CommandText property. Cancel: Cancels an execution of a method. Record Object: It allows you to run commands against the data store. It is used to execute a single query against a database. The query can perform actions like creating, adding, and retrieving, deleting or updating records. The Record object is used to represent a record in a recordset, or to represent a file or even a folder in a file system or an email message in an email folder structure. The syntax to create a Record object in ASP: Dim objRec Set objRec = Server.CreateObject("ADODB.Record") If you wanted to use the Record object to handle the files and folders on your web server, you could use the Open method, passing a URL on your web server, like this: objRecord.Open "Delete.asp", "URL=http://chrisu/BegASP/"

This method takes two arguments: the first is the file or folder that we're looking for and the second is the URL to which any actions will apply. Properties: ParentURL: Returns the absolute URL of the parent Record. RecordType: Returns the type of a Record object. State: Returns the status of a Record object. Methods: Open: Opens an existing Record object or creates a new file or directory CopyRecord: Copies a file or directory to another location. MoveRecord: Moves a file or a directory to another location. DeleteRecord: Deletes a file or directory. Close: Closes a Record object. Stream Object: It allows the manipulation of data held in web resources, such as HTML files. The Stream object is used to represent the most basic denomination of data – binary data or just plain text. The syntax to create a Stream object in ASP: Dim objStr Set objStr = Server.CreateObject("ADODB.Stream") We use its Open method to open the object on a data source and hence access the stream of data contained within: objStream.Open "http://chrisu/BegASP/ReadMe.txt", adModeRead, adOpenStreamFromURL This example opens the Stream object on the stream of text contained in the file ReadMe.txt, which is contained in a virtual directory of my web server machine. Properties: State: Returns a value describing if the Stream object is open or closed. CharSet: Sets or returns a value that specifies into which character set the contents are to be translated. This property is only used with text Stream objects (type is adTypeText). EOS: Returns whether the current position is at the end of the stream or not. Methods: Open: Opens a Stream object. WriteText: Writes character data to a text Stream object. ReadText: Reads the entire stream, a line, or a specified number of characters from a text Stream object. Close: Closes a Stream object

Communication Information: Each time you communicate with a data store, you need some form of connection. There are three steps to supply information while creating a connection: Step 1:- Connection String It is a simple character string that lists all information needed to connect to a source of data. It contains all of the following information: • Provider : type of OLE-DB provider used in the connection • Driver : type of ODBC driver • Data Source : physical database path and file name • Initial Catalog : name of the database • User ID : user name needed to connect to the database • Password : password of user specified in the User ID • Persist Security Info : a Boolean, set to True if you want Windows to remember your password A Sample Connection String: If we're connecting to an Access database then we might use a connection string like the following (this is the connection string from the Connect.asp example above): "Provider=Microsoft.Jet.OLEDB.4.0; " &_ "Data Source=C:\datastores\Movie2000.mdb;" & _ "Persist Security Info=False" Step 2:- Data Link file It is a method for connecting to your data store which helps to avoid the need to type all of the code into a connection string by hand. In Windows Explorer in Windows 98 or NT 4.0, you could create a data link file by selecting the New option from the File menu – and thus generate and store the necessary connection string information in a UDL (Universal Data Link) file. Since then, Microsoft has deemed the ready accessibility of this functionality as 'confusing' to novices, and has thus partially removed it from Windows 2000. Step 3:- DSN The Data Source Name (DSN) is another way to establish your connection string without typing it explicitly – again, it involves getting Windows to do most of the hard work for you. DSNs boast the advantage that they are very simple to use. However, DSNs are now considered to be an outdated method of establishing a data connection. Unfortunately they use ODBC drivers – so you lose many of the advantages that come with using the OLE-DB providers, because DSNs don't support them.