What are the "must have" features for a XML based GUI language

Question

Summary for the impatient:

What I want to know is what you want to have in a new gui language. About the short answers mentioning $your_favorite_one; I assume you mean that, such a language should look like $your_favorite_one. These are not helpful. Resist the temptation.

I'm thinking on the user friendliness of XML based languages such as XHTML (or HTML, although not XML they are very similar), XUL, MXML and others ("others" in this context means that, I am aware of the existence of other languages and their implementations alternative to their original ones, and the purpose of the mentioning only these languages by name is, to give an idea of what I am talking about and I don't feel like mentioning any others and also, I see no point in trying to make a comprehensive list anyway.). I have some opinions about what features should such a language have;

1. The language should be "human writable" such that, an average developer should be able to code a good amount without constantly referring which tags have which properties, what is allowed inside what. XHTML/HTML is the best one in this regard.
2. There should be good collection of controls built-in for common tasks. XHTML/HTML just sucks here.
3. It should be able to be styled with css-like language (with respect to functionality). It should be easy to separate concerns about the structure and eye-candy. Layout algorithm of this combined whole should be simple and intuitive. Why the hell float removes the element from the layout? Why there is not a layout:not-included or something similar instead?

I know that I don't even mention very important design considerations like interaction with rendering engine and other general purpose languages, data binding, strict XML compliance (ability to define new tags? without namespaces?) but these are the points that I would like to ask what you consider important for such a language?

Answer 1

I would like it to be easy to connect to any database, perform queries that return a recordset, and be able to parse and iterate easily said recordset to display its data in graphic controls, for example pie-charts, bar-charts, timeline charts (stock options like), node graphs with animation effects, all this at run time.

Easy mouse events catching, to implement any action on rollovers, mouseins, mouseouts, clicks, drag and drops, clipboard management, etc. A good infinite zooming capability would be great too.

I don't want to set a "datasource" that establishes a fixed connection between some column in my SQL query and some displayable element at design time, I want to perform any query that I want and show elements tied to any query field, anytime, in run time. I don't want to be only able to bind a datasource and displayable elements at design time.

css style capability for everything. Or something as simple and easy.

resize and layout taken care of automatically. Easy access to local files, to parse, play, display. Easy classes for image management, supporting transparency, resizing, etc. Basic and advanced classes for drawing in the screen: lineTo, rectangle, circle, animations. Even 3D.

Embedded fonts functionality. I don't want to worry about "will the user have this font installed?" Also I don't want to worry about DPI or screen resolutions.

Basic widgets: treeviews, etc.

A good designer. I don't want to add widgets writing the code. I want to place them visually in the screen.

Also, it would be good if it could connect to dlls made in C++ or COM objects in general.

Answer 2

Most recent XML GUI language (not only for GUI actually) is called XAML. It has all that candies: styles, layout definition, objects initialization, etc. But it's a pain to write more or less large XAML files. Auto-completion helps but the core problem - forest of angle brackets - is not solved. Another problem with advanced XML-based GUI langs - they try to serve to several purposes at once, but XML syntax is not suitable for all situations. For example XAML supports data-binding, but why the hell I should write it in attribute string? It's first class feature and should have proper support.

IMO all modern XML-based langs suck terribly. Language intended for humans must not force it's users to write tons of brackets or do deep tags nesting. It must be user friendly, not computer friendly. My dream it to have GUI language with Python-like syntax.

In conclusion I want to say:

Dear XML-based langs authors, please be humane, don't create another language based on XML. Read some good book on Domain Specific Languages and please, don't make me type < and > symbols ever again.

Answer 3

There will always be a tradeoff between ability and simplicity.

Personally I'm happy with the features of WPF (which uses XAML) for MS development. I dont find its complexity to be a barrier to developement at all.

However if your going to target your toolkit/language to a demographic that requires a higher degree of simplicity, you could possibly get away with leveraging an existing framework and provide the end user with a DSL specific to their needs.

Writing a new framework for the dev community as a whole is a mammoth undertaking though, and I suspect you will find that due to the wide range of features required that you will have to deal with a large degree of complexity at some point. Best of luck.

Answer 4

You should have specified whether you mean web or rich client, but either way take a look at XAML/WPF. If you're anti-MS, then look at Moonlight, the Mono implementation of SilverLight.