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Visual InterDev and Friends
By John M. Telford
Internet Systems , April 1997
An Up-Close Look at Microsoft's Long-Awaited Web Application Development
Tool.
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Like a cat with nine lives, Microsoft Corp.'s often-renamed and
reincarnated Web application development tool is back again, and this
time it's really shipping. Microsoft's Visual InterDev product, formerly
code-named Internet Studio, is a tool for Web developers who build
complex and intensive Web client/server applications. Visual InterDev
centers around a visual development environment that integrates all of
the tools necessary to build and deploy complex and intensive Web
applications.
The Visual InterDev Web development tool is aimed at Web (Internet and
Intranet) database developers. Web authoring tools such as Microsoft
FrontPage, Sausage Software HotDog, SoftQuad Inc. HotMetal Pro, and
Netscape Communications Corp. Navigator Gold and Composer in the new
Communicator suite are intended more for Web content authors than Web
developers. These tools may provide some support for adding applets and
scripting to Web pages, but they focus on giving Web content authors
tools to build and manage sets of Web pages. Many of those Web authors
never go near a database.
Visual InterDev supports building server-side applications using a new
feature of Microsoft Internet Information Server (IIS) 3.0 called
Microsoft Active Server Pages (ASPs, formerly code-named "Denali"):
ASCII text files containing text, HTML, and scripts. ASPs are prototypes
for server-side processing of database access, state management,
server-side scripting, and reusable server components. Visual InterDev
also has built-in database development tools that enable access to any
database supporting ODBC.
Visual InterDev includes Web site-management tools, such as a
visualization tool for ongoing site-management tasks. Visual InterDev
also includes a version of the FrontPage WYSIWYG Web authoring HTML
editor, as well as tools for developing Web-based images and sound
effects.
Web developers can use Visual InterDev to build complex and intensive
Web client/server applications accessible by any Web browser on any Web
client. The development tool itself runs on Windows 95 and Windows NT
Workstation 4.0. A Visual InterDev Web client/server project is stored
on a Microsoft Personal Web Server running on Windows 95. It can be
stored on a Microsoft Peer Web Services Version 3.0 running on a Windows
NT workstation; it can also be stored on a staging or production
Microsoft IIS 3.0 running on a Windows NT Server. During file editing,
Visual InterDev retrieves files from the Web server and places them into
a working directory on the developer workstation. Visual InterDev makes
extensive use of ASPs.
Web Client/Server Applications
Step back a minute to understand what led Microsoft to the design
decisions embodied in Visual InterDev. Evolving into something more than
a medium for publishing static billboard-style documents, the Web is
emerging as the next incarnation of client/server. Early on, clever
people figured out ways for Web browsers to invoke processes on Web
servers and pass parameters at the same time. Web server processes
returned output to Web browsers as HTML pages. The Common Gateway
Interface (CGI) standard grew out of this work, and Web client/server
began.
Contemporary Web client/server focuses on the Web client side.
Microsoft, Netscape, and others seem to be promoting creating fat Web
clients by encouraging Web developers to stuff Web browsers with ActiveX
components, Java applets, JavaScript, and VBScripts. Doing so helps with
distributed systems management realities. Everywhere you look, Web
client/server is being described as a "killer" technology on the
Internet. Unfortunately, it is also killing Web browsers. Web servers
are force-feeding browsers more and more complex information.
There is a better way, however. The server side of a Web client/server
application is the appropriate place to use ActiveX, ADC, DCOM, IIOP,
Java, JDBC, JScript, VBScript, and other technologies such as
Microsoft's Transaction Server (previously known as "Viper). There,
scaling computing resources is more economical. In a way, it is
déjà vu all over again; we have gone full circle, from
central computing to distributed computing and back to central
computing. This time around, the dumb terminal of yesteryear is no
longer dumb. It is a workstation running a server-independent Web
browser and using public-domain TCP/IP network technology. A lot of the
legacy blatant proprietary lock-in technology has gone undercover with
the coming of Web client/server technology. Some vendors now mask
lock-in devices under the cloak of "Open" something or other.
It is possible to do almost everything on an IIS 3.0 Web server using
ASPs. Taking this approach means that complex and intensive Web
applications are accessible to the most humble of Web clients as long as
they have enough steam to run a Web browser. This may be an important
consideration with emerging Network Computer (NC) technology driven by
anti-Wintel and the Wintel NetPC initiative. It is too soon to tell.
Using Visual InterDev is an excellent way for Web developers to create
and maintain complex Web client/server applications using ASPs. Of
course, Visual InterDev is also an excellent way to develop complex Web
client/server applications requiring Web servers to force-feed
already-fat Web clients. The choice is yours.
Active Server Pages
ASPs are a new addition to IIS 3.0. ASPs provide a Web server-side
scripting environment. Web client/server application developers use ASPs
to create and run dynamic applications. The Web server does all the work
of generating HTML pages when scripts are processed there and sent on to
the Web browser.
Web client/server application HTML development and scripting development
become the same process when using ASP. Developers embed both HTML and
script statements within the same ASP file. IIS 3.0 includes native
support for VBScript and JScript, Microsoft's answer to Netscape's
JavaScript. IIS 3.0 also supports other scripting languages such as
PerlScript, Python, and REXX through Active Scripting plug-ins.
ASP uses the <% and %> delimiters to enclose script commands and the <%=
and %> delimiters to enclose output expressions. These delimiters
differentiate script commands from text, HTML tags, and Web client-side
scripting. The IIS 3.0 Web server checks for an .asp filename extension
when a Web browser makes a request. When the Web server detects an ASP
file, it searches for the <% and %>, and <%= and %>, delimiters in the
file. It processes any code between them and writes any generated output
to the output buffer. The Web server copies anything not between the
delimiters directly to the output buffer. In other words, you can have
VBScript processed by the Web server, and VBScript passed through the
Web server without processing, in the same ASP file. When the Web server
finishes processing the ASP file, it sends the contents of the output
buffer to the Web browser. The default scripting language for ASP is
VBScript. ASPs use just-in-time compiling technology to compile Web
server-side scripts to byte code automatically on an as-needed basis.
Changes made to a Web server-side script cause the compilation process
to happen automatically.
Server-side scripts can perform a number of tasks by using objects built
into IIS 3.0 ASPs. These tasks include gathering information from the
user, retrieving data from a database, and dynamically constructing HTML
pages that are returned to the Web browser. Five built-in ASP objects
are Application, Request, Response, Server, and Session. The Application
object enables information sharing among all users of an ASP Web
client/server application.
The Request object retrieves values of parameters that Web browsers pass
to the IIS 3.0 Web server during an HTTP request: It stores them in
object collections. The Request object collections are values of fields
stored in the client certificate, values of cookies, values of form
elements, values of variables in the HTTP query string, and values of
predetermined environment variables. The following ASP snippet outputs
the value of Monster cookie to the Web browser:
<BR>The value of the cookie named Monster is:
<%= Request.Cookie("Monster") %>
<BR>
The Response object enables you to manipulate the HTML and HTTP sent
back to the Web browser. The Response object collection lets you specify
cookie values. The Response object properties are output buffer
information, HTTP content type, Web browser page-caching time, and ASP
return status. The Response methods let you set HTML headers, append to
the Web server log, and erase buffered HTML output. They also let you
stop ASP file processing, flush the output buffer, send and redirect
messages to the Web browser, and write a variable to the output buffer.
The following ASP snippet uses the Request.Form method to retrieve the
value of the yourname element from the form collection and then writes
it to the output buffer:
<BR>Hello, your name is: <% Response.Write Request.Form("yourname") %>
The Server object provides access to methods and properties on the Web
server. Most of the methods and properties are utility functions. The
Server object property is the amount of time the script can run before
it times out. The Server object methods create an instance of a server
component, apply HTML encoding to a string, map a virtual path, and
apply URL encoding rules. The following ASP snippet sets the maximum
amount of time the script can run before it times out to 60 seconds:
<% Server.ScriptTimeout = 60 %>
The Session object stores state information needed for a user session.
Variables stored in the Session object are not discarded when the user
jumps between pages in the Web client/server application. Session
variables persist for the entire user session. The IIS 3.0 Web server
automatically creates a Session object when a Web browser requests the
first .asp page. The Web server destroys the Session object when the
session expires; it also destroys the Session object when the Web
browser abandons the session. Session state information is only
maintained for Web browsers that support cookies.
The Session object properties are the session identification for this
user and the time-out period for the session. The Session objects single
method destroys a Session object and releases its resources. The Session
events are Session_OnStart and Session_OnEnd. The following ASP snippet
causes the session state to be released when the server finishes
processing the current page:
<% Session.Abandon %>
ASP also supports IIS 3.0 Web server components (or automation servers).
These components are Ad Rotator, which automatically rotates
advertisement displays; Browser Capabilities, which determine Web
browser capabilities; Content Linking, which creates tables of contents
for a Web client/server application; and File Access.
Web Client/Server Tools
Legacy RAD tools do not work for developing Web client/server
applications. Legacy client/server tool vendors scrambled to reinvent
themselves and their tools to meet the demands of the emerging Web
client/server marketplace, and many of these legacy tool vendors are
already shipping add-ons and successor products.
The underlying network and UI technologies for Web client/server
applications are fundamentally different from legacy client/server
applications. Web client/server applications use HTTP network
connections to Web servers. These network connections are established,
broken, and re-established as the Web browser requests HTML pages and
other objects over the network. Legacy client/server applications rely
on persistent network connections between the client and server. Web
client/server applications use Web browsers as clients and a GUI based
on a workstation.
Developers use Visual InterDev at design time to create and edit ASPs.
They embed scripts within them using JScript, VBScript, PerlScript,
Python, or REXX. The following ASP snippet contains HTML and VBScript;
it passes through the IIS 3.0 Web server to the output buffer without
processing.
The developer workstation maintains an ODBC connection to the Web
client/server application database server over a Local Area Network
(LAN) at design time. The developer workstation functions as a client of
the database server in a traditional client/server way.
Web Database Development
Visual InterDev database development components are an integrated data
view, database design-time ActiveX controls, database wizards, and a
database designer. Visual InterDev built-in database connectivity is
based on the ODBC standard. Any database supporting ODBC, such as
Oracle, Microsoft SQL Server, Microsoft Access, Microsoft Visual FoxPro,
Informix, Sybase, and IBM DB/2, will work with Visual InterDev. The
Visual InterDev database access tools are based on Microsoft ActiveX
Data Objects (ADO), which provides flexible, object-based database
connectivity to ODBC data sources.
ActiveX Data Objects is a new Microsoft data access programming model.
If you are familiar with Data Access Objects (DAO) or Remote Data
Objects (RDO), you will recognize the ADO interfaces and be readily able
to work with them. Active Data Objects are specifically designed for Web
client/server data access. They provide an object-based approach to
accessing data over the Web. You can establish database connections to
any ODBC data source through ASP scripting. You can select
database-defined datatypes -- such as binary large objects (BLOBs) and
.gif and .jpg images from databases -- and then write them to the ASP
output buffer using ASP scripting. Other ADO properties are setting
locking levels, cursor options, query and login time-outs, transaction
support, resultset scrolling, and error handling.
The Data View feature gives you a visual interface to all of the
databases being used within a Web site. It depicts each database
connection being used in the site and provides a live connection to each
database so that you can work directly with these databases within the
IDE.
Visual InterDev provides built-in components, Wizards, and design-time
ActiveX Controls to generate much of the ASP scripting. They generate
the necessary scripting and ADO calls to establish database connections,
perform queries, and display results, within a Web client/server
application. You can use design-time ActiveX Controls to create
data-driven Web client/server applications with little additional
programming. You can also choose not to use design-time ActiveX Controls
and instead develop and optimize ASP scripting and ADO calls yourself.
The Database Designer is a special feature of Visual InterDev. Based on
the Visual InterDev extensible architecture, the Database Designer lets
you create database diagrams and key relationships between tables. It
has the graphical ease-of-use of Microsoft Access to set up and
administer Microsoft SQL Server databases without leaving the Visual
InterDev IDE. Support for other database systems will most likely be
added in the future.
Web Site Management
Visual InterDev offers several site-management features. Web site
Wizards step the Web client/server developer through the process of
creating new Web sites on Web servers that support Visual InterDev
extensions. Developers can add, copy, delete, rename, and edit any file
in the Web site. Developers can import files into a Web site from any
local or network resource. You can move an entire Web client/server
application from one Web server to another, which makes it relatively
simple to utilize staging and production Web servers. Links among Web
pages within a Web client/server application are automatically
maintained by Visual InterDev when Web pages are moved or renamed.
Visual InterDev has a Web visualization tool called Link View that
presents a graphical view of Web client/server applications. I should
note here that Microsoft recently announced its acquisition of NetCarta
and will incorporate NetCarta into BackOffice and IIS as another way to
navigate or display the structure of a Web site.
Developer organizations can use Microsoft Visual SourceSafe 5.0 with
Visual InterDev for Web client/server project source control. Visual
SourceSafe is not required to be installed on the developer workstation.
All Visual SourceSafe features execute on the Web server.
Bottom Line
Microsoft Visual InterDev, like IIS 3.0, is an excellent tool for Web
developers to create and maintain substantive Web client/server
applications. It is an interactive, integrated Web client/server
application development environment. Developers using Microsoft C++ and
Microsoft J++ will be so familiar with the Visual InterDev IDE that
they'll be able to create Active Server Pages, ActiveX components using
C++, and Java Applets using J++ -- all in the same Visual InterDev IDE
and all at the same time. Microsoft has also integrated database
connectivity options and visual database tools into Visual InterDev.
Microsoft can improve Visual InterDev by integrating client- and
server-side debugging into the product. The company could also improve
state management. One way would be to generate a unique token that
identifies the Web client/server application and the Web client, store
this token in a cookie, and use it as a Registry key. Web developers
could use the Registry to store arbitrary Web client information between
sessions without using the Web client/server database.
Microsoft has set the standard for an interactive, integrated Web
client/server application development environment. Other vendors in the
Web tool marketplace now have a product to meet or beat.
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John Telford is a distributed systems architect, software practitioner,
and project manager. He formed InfoMax Consulting more than five years
ago and has have been working in the computer business for more than 30
years. You can email John at jmt@infomax.com or contact him through his
Web page at home.sprynet.com/sprynet/jmt/infomax.htm.
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Figure 1
[IMAGE][3]
--A rendering of an HTML script snippet in Microsoft Internet Explorer.
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[1] http://www.dbmsmag.com/9704i04.html
[2] #figure1
[3] http://intranet.www-kr.org/hn/intranet/17/9704i041.gif
