Three options for Web Data Retrieval

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Three options for Web Data Retrieval

• 3 technologies let you connect to remote data
  sources and invoke methods without leaving the
  current page.

Dino Esposito desposito_at_vb2themax.com
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Agenda

• Remote Scripting
• DHTML Data Binding
• Remote Data Services
• Annotated Overview

This presentation assumes youre familiar with
DHTML and JScript. A knowledge of scriptlets
would help.
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We have a problem...

• Migrating the C/S metaphor to the world of Web.
• Migrating a stateful metaphor to a stateless
  protocol such as HTTP.
• Any request to the server means a new page to be
  sent to, and displayed by, the browser.

Reduce the traffic over the network, Simplify
state maintainance, Increase the responsiveness
of the application
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We have a solution...

• A typical schema that youve probably implemented
  countless times...

IIS
Default.asp
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It has to be a better way...

• A way in which you just issue remote calls, get
  the results and update the current page.

IIS
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Remote Scripting

• Library of script functions (mostly) based on
  JavaScript.
• Lets you call public methods from an ASP page.
• You can do that from either a client-side HTML
  page and another server-side ASP page.
• Remote Scripting (RS) is included in Visual
  InterDev 6.0.

rs.htm Client-side proxy rs.asp Server-side
stub rsproxy.class Transportation layer
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Using RS on the client

• Initialize the RS engine by calling
  RSEnableRemoteScripting()
• Include the rs.htm file in your page.
• Call RSExecute() to invoke (sync/async) a remote
  method.
• You are returned a structure with the return
  value and possible error messages.
• You can get a local copy of the remote object.
  Object-based vs. Function based syntax.

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Using RS on the client
lt!-- typical header for a RS-enabled HTML page
--gt ltBODYgt ltSCRIPT language"JavaScript"
src"http//expoware/_ScriptLibrary/rs.htm"gt lt/SCR
IPTgt ltSCRIPT language"JavaScript"gt
RSEnableRemoteScripting("http//expoware/_ScriptLi
brary") lt/SCRIPTgt function execSynch() var
co RSExecute(pageURL, "GetEmpInfoAsArray",
frm.empName1.value)
refreshPage(co)
aspObject RSGetASPObject(pageURL) function
execSync() var co aspObject.GetEmpInfoAsArr
ay(empName1.value)
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Using RS on the server

• Invoke the RS method dispatcher at the top of any
  ASP page RSDispatch.
• Include the rs.asp file in your page.
• Define a public interface for the functions
  externally callable
• Such an interface is based on an object with a
  fixed name public_description. A JS or VBS 5.0
  class.

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Using RS on the server
lt!-- typical header for a RS-enabled ASP page
--gt lt RSDispatch gt ltSCRIPT RUNATSERVER
languagejavascriptgt lt!--INCLUDE
VIRTUAL"/_ScriptLibrary/RS.ASP"--gt function
Description() this.GetEmpInfoAsArray
DoGetData public_description new
Description()
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RS Architecture
IIS
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RS in action

• How to access the Employees table in the
  NorthWind database and display the data for a
  given employee.

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Cross-browsing

• RS is based on JavaScript
• Uses a Java applet to communicate with the remote
  ASP page
• It works on any Java/Javascript-enabled browser
  and any Web server that supports ASP

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DHTML Data Binding

• Supported by IE 4.0 and higher, data binding (DB)
  is the Web counterpart of Visual Basic's
  data-bound controls.
• Data binding lets you bind a data source with one
  or more HTML tags on a page.
• You dont have to take care of the connection or
  retrieving and marshaling a recordset.
• The loading of the data is asynchronous.

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Using Data-binding

• You need to embed an ActiveX control to govern
  the operation. You need to use its DHTML ID to
  link to HTML elements.
• For any tag to bind, specify the DATASRC and
  DATAFLD attributes. They link the element to a
  field in the data source.
• You connect to a data source through the
  properties of the ActiveX control.

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Using Data-binding
ltOBJECT style"displaynone" id"rds"
classid"clsidBD96C556-65A3-11D0-983A-00C04FC29E3
3"gt lt/OBJECTgt ltSPAN DATASRC"rds"
DATAFLD"employeeID"gtlt/SPANgt rds.Server
"http//expoware" rds.Connect "DSNNW"
rds.Sql select from employees"
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Data-binding Architecture
ltobject idrds...gt lt/objectgt ltspan
datasrcrds datafldemployeeIDgt lt/spangt
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Data-binding in action

• Working with single tags
• Working with HTML tables
• Using a DHTML scriptlet to format a table
  on-the-fly
• Access to any OLE-DB provider.

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Remote Data Services

• RDS comprehends a couple of controls that
  provides the third way to get data through the
  Web without leaving the current page
• DataSpace, DataFactory
• RDS issues calls to COM objects located on the
  Web server.
• You need to know the progID of the object
• RDS brings COM far beyond DCOM

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How RDS works...
IIS
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RDS in action

• Using the DataSpace and the DataFactory objects
  to create remote HTTP-based instances of COM
  objects and get recordsets.

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More on RDS

• Youre still working over stateless protocol.
• Any remote method invoked requires a new
  roundtrip.
• Any state held between two calls, gets lost.
• Design stateless components to work with RDS

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Annotated Overview 1

• Remote Scripting
• ? Works with Netscape, ? Best with DHTML
• No knowledge of COM required
• Completely script-based
• Object mirroring
• Both synchronous and asynchronous calls
• Require page modifications

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Annotated Overview 2

• Data Binding
• ? Easy to use, ? Requires IE4
• Not suitable if youre getting raw data to
  manipulate before displaying
• Easy to componentize through DHTML Scriptlets
• Allows local sorting and filtering
• Allows raw text and HTML
• Association between tags and data sources

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Annotated Overview

• RDS
• ? Based on COM, ? Requires MDAC 2.1
• Less page intrusive than RS or DB
• Lets you think in terms of components
• Part of the Microsoft Windows DNA
• Doesnt allow asynchronous calls
• Support HTTP and HTTPs

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References

• Remote Scripting
• Cutting Edge, http//www.microsoft.com/mind
• http//msdn.microsoft.com/scripting
• http//msdn.microsoft.com/voices/scripting.asp
• http//www.asptoday.com
• DHTML Data Binding
• Cutting Edge, http//www.microsoft.com/mind
• http//www.asptoday.com
• Remote Data Services
• http//www.asptoday.com
• Professional ADO RDS with ASP - Wrox Press

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Q A