Integrating applications and the World Wide Web

Abstract:

This paper describes how to integrate the World Wide Web (WWW) with applications. By means of the web widget, which is part of Hush, the WWW is made available to Tcl/Tk/Hush programmers. Apart from using WWW as part of an application, it also allows one to embed scripts into a web page. This results in a mutual integration of applications and the WWW.

Both forms of integration will be described. Some new possibilities of embedded scripts such as inline MPEG, interactive games and navigation facilities will be discussed.

Keywords:

WWW, embedded scripts, integration, Hush, Tcl/Tk

What is Hush?

The Hush library is intended to support the needs of both novice and experienced (window) programmers. Although Hush can be used to write all sorts of programs with a graphical user interface, it mainly focusses on hypermedia applications (i.e. the combination of hypertext and multimedia).

Currently Hush provides several hypermedia extensions, including a MPEG widget. MPEG is a widely used video standard. Hush also includes a C++ API and a Tcl interface [Music94] for Csound, a software sound synthesis package developed at MIT's Media Lab. Another extension is the web widget, described in this paper, which gives access to the World Wide Web.

World Wide Web

An important feature missing in current WWW browsing systems is the lack of integration with other applications. That should change, because the WWW can be a very valuable part of an application [Ercim94]. This paper describes two forms of integration:

• Integrating WWW in applications (use WWW as part of a program).
• Integrating applications in WWW (embedding scripts in a WWW page).

Using WWW as part of an application

The Tcl/Tk/Hush environment offers numerous widgets which can be used to build a graphical user interface, e.g. button, scrollbar and listbox. These widgets are not only accessible from a Tcl script, but also from C++ (because of the Hush API). The web widget is a new widget, implemented in C++. It can be used exactly the same way as a standard widget in Tcl/Tk.

The following Tcl-script builds a very simple WWW browser by creating a web widget together with a back button:

    web .w -home "http://www.cs.vu.nl/"
    button .b -text "Back" -command {.w back}
    pack .w
    pack .b

The previous example was written in Tcl. In C++ the same functionality can be achieved as follows:

    web *w = new web(".w");
    w->home("http://www.cs.vu.nl/");
    button *b = new button(".w", "-command {.w back}");
    b->text("Back");
    w->pack();
    b->pack();

The web widget makes it possible to access the WWW from within an application. It can be used to view HTML files which are stored locally, but because of the network facilities the information can also be retrieved from servers all over the world. For example, it is possible to provide all on-line help as WWW-pages. Advantages of this approach are:

• All help can be written in HTML, which is becoming a standard markup language.
• Help is not limited to text, because images, animations etc. can be used.
• The on-line help files can be stored in one location. Users from all over the world can access this information, without even noticing they are getting it through the network. This will enable application builders to change the on-line help information, e.g. provide up-to-date FAQ (frequently asked questions) lists, correct errors in the help text, announce patches or new versions etc.
• The help information will also be available separate from your application. Future users can get access to the on-line help by using browsers like Mosaic, even though they have not installed the application (yet).

Of course usage of the WWW within an application is not limited to on-line help. It can also be used to provide other information, to represent the output of some processes (e.g simulations) or the web widget may simply be used for it's hypertext capabilities without employing the network.

Because the web widget itself runs in the same Hush environment as the program, the look-and-feel of the browser can be adjusted to fit the needs of the situation.

Embedding scripts into WWW pages

Most graphical based WWW browsers support inline images with the <img> tag. Using inline images can result in attractive web pages. It would nice if other kind of objects could be embedded as well (for example videoclips). Allowing to embed an arbitrary script with commands is even better, because this way almost anything can be included as an inline object in a web page. Otherwise a new version of a browser should have been made to enable the embedding of a new kind of object.

The web widget makes it possible to embed an arbitrary script. The script is executed when the page is displayed. Currently only Tcl-based scripts can be used, but using other languages should be possible as well, because the Hush framework also supports other script languages.

To include a Tcl-script in a web page, HTML is extended with a new tag <hush>. It supports an attribute 'tcl', which contains the Tcl code that will be executed. For example, to include a button in a web page, the following HTML code can be used:

    <hush tcl="button $$this.b -text {Hello}; pack this.b">
    </hush>

    <hush tcl="...">
    Sorry, this browser does not support the <em>hush</em> tag.
    </hush>

    <hush tcl="source /usr/local/demo/mpeg.tcl">
    Sorry, this browser does not support inline MPEG
    </hush>

    <hush tcl="exec audioplay [urlfile www.cs.vu.nl/sounds/tune.au] &">
    </hush>

    <hush tcl="button this.b -text Back -command \"$$thiswidget back\"; pack this.b">
    </hush>

    <hush tcl="source /usr/local/www/tcl/inline.tcl">
    Sorry, this browser does not support embedded scripts.
    </hush>

    <hush tcl="source [urlfile www.cs.vu.nl/tcl/inline.tcl]">
    Sorry, this browser does not support embedded scripts.
    </hush>

    button $$this.m -bitmap "@[urlfile www.cs.vu.nl/images/press_me.gif]"
    pack this.m