Hi!

On 9/21/07, Vincent Massol <vincent@massol.net> wrote:
Hi Mikhail,

Thanks for sharing this info with us! This makes it more clear for me.

From what I understand below you're recommending to eliminate the need for TextProcessor and instead do the following:

* Store the documents in the database in the DOM format (XML)
* Store scripts as a verbatim block in that DOM
* Only use DOMProcessor to make transformations to the DOM. For example have a VelocityDomProcessor and GroovyDomProcessor to modify the script DOM elements and evaluate them. 

Exactly. It should be much faster and these scripts will work with typed objects (WikiDomNodes) and not with a plain text.

Note: Velocity or Groovy scripts can generate wiki syntax content and thus these would need to generate new DOM elements. Not sure how easy that would be.
I think that with Groovy it can be even simper to work nodes than with Velocity.
An example:
-------------------------------------
// Velocity:
-------------------------------------
<div>
<h1>Hello $customer.Name!</h1>
<table>
#foreach( $mud in $mudsOnSpecial )

   #if ( $customer.hasPurchased($mud) )
      <tr>
        <td>
          $flogger.getPromo( $mud )
        </td>
      </tr>
   #end
#end

</table> 
</div>
-------------------------------------
// Groovy:
// (see http://groovy.codehaus.org/GroovyMarkup
, 
// http://groovy.codehaus.org/Builders)
-------------------------------------
def xml = new MarkupBuilder()
xml.div() {

  h1("Hello, ${$customer.Name}!")
  table() {
    for (mud in mudsOnSpecial) {
      if (customer.hasPurchased(mud)) {
        tr(){ td( flogger.getPromo(mud) ) }
      }
    }
  }
}

-------------------------------------

From my point of view the second example is even simpler then the Velocity-based one.
The advantages of the Groovy-based stuff:
- It generates a well-formed HTML (you have no choice, it is done automatically :-))
- It can be compiled directly to the Java bytecode and cached
- It is much more powerful then Velocity
- You don't have to learn 2 stuff at the same time - Velocity and Groovy
- It is possible to write WikiModel specific builders which will be much more efficient then the generic MarkupBuilder from the example above. It will be possible to manipulate with, say, tables in the following way: table[i][j] = "Hello!";

I think that in any way you have to be a geek to write a template :-). You have to understand at least some notions like "variables", "if" conditions, "for" cycles and so on. And IMHO it is simpler to use these structures in a normal programming  language. And if you are a "normal" user then for you even Velocity templates are completely unreadable.
Another aspect is that if you have errors in your Velocity template it don't save you from exceptions. It it doesn' work in the same way as a bad-written groovy code :-).

This means the VelocityDomProcessor would need internally to use a Parser to parse the result of the evaluation and generate a sub-DOM. Is that correct?

Exactly.
 

Thus the textual format would only be used when the user enters text or when we want to export the content.

Yes

The main advantage would be performance since there'll be no need to go back and forth between textual format and DOM format.

Not only. Other advantages:
- Results are well-formed (you manipulate with objects and not with plain text).
- Resulting graph can be serialized in *any* format (PDF, ps, XML, wap, ...); You don't have plain HTML, you control all aspects.

Makes sense to me.

Fine.

Now you mention removing Velocity. This won't be possible since all current XWiki instances used are using Velocity and we cannot tell our users that they have to rewrite all their pages if they want to move to XWiki v1.3. We'll need to continue supporting Velocity for some time. Personally I currently find that the velocity syntaxes mixes much better with the wiki syntax than groovy. If you look at contributed code snippets you'll see that most are in Velocity which is what most people use.

In any case if you change the syntax you will have to process your scripts as well. 
Maybe it would be possible to create a  translator from Velocity to Groovy:
- Take a page containing a velocity template
- Parse it using Velocity and produce in-memory JST representation of this template (Velocity is JavaCC based it uses abstract syntax trees...)
- Launch a visitor translating each individual structural element of this template to the corresponding Groovy code. (see http://svn.apache.org/viewvc/velocity/engine/branches/Velocity_1.5_BRANCH/src/java/org/apache/velocity/runtime/visitor/ )

About the usage of Groovy and templating... I don't like at all the groovy templates where the syntax like <% if (...){%>Hello<%}%>  is used. It is "inspired" by bad-styled JSP/ASP/PHP... But I really like Groovy builders, as I wrote above. And I have impression  that these builders can easily replace Velocity (or other templates).

Now you mention other stuff about Jasper and Jetty but I'm not sure I have understood that part.

I thought that it would be possible to use the JSP syntax to create templates. So each wiki page can be considered as a jsp page (maybe - if it contains some specific markers in the content) and it can be parsed and compiled as a JSP. The advantage:
- And, especially, usage of standard tag libraries (like <c:forEach items="${addresses}" var="address">...</c:forEach>) The standard tag libraries gives the same functionalities (and much more) than Velocity. The advantages: it is a standard, it can be compiled directly in java, ...
- Usage of multiple languages (javascript, jpython, jruby, groovy...) if you use the syntax like "<% if (...) {%>Hello!<%}%> (I hate this coding style!)

Personally I would like to see the Groovy templating much more than JSP-based one. It was just a proposal...

Best regards,
M

Thanks
-Vincent

See below.

On Sep 19, 2007, at 6:54 PM, Mikhail Kotelnikov wrote:

Hello!

Just some words about what the wiki model is and what it is not.

The main goal of the WikiModel is the creation of an API giving access and control to the internal structure of individual wiki documents.

Some features of the WikiModel:
- WikiModel itself does not depend on any particular wiki syntax
- The number of possible structural elements and their possible assembling order is strictly fixed (which greatly simplifies the validation and manipulation) but the final result is almost as expressive as XHTML (and even more expressive, taking into account notions of properties and embedded documents which can recursively contain their own embedded documents :-)).
- WikiModel manipulates with a super-set of structural elements available in existing wikis. And it has some features not available in other wikis. For example using embedded documents in WikiModel it is possible to put a table in a list and this table can contains its own headers, paragraphs, and lists... Or using embedded documents with the notion of properties it is possible to define very complex structured objects directly on a wiki page.
- There is at least one wiki syntax ("Common" syntax) giving access to all features of the Wiki Model. This syntax guaranties that all structural elements of the WikiModel can be serialized/de-serialized without loose of information and structure. Using any other syntaxes can lead to the information lost (example: you can not put table in a table in XWiki or in JSPWiki which is possible using the Common Syntax).
- One of the goals of the WikiModel is to give a mean to *import* information from various wiki engines without information lost. The structure of documents can be serialized in various wiki syntaxes as well, but there is no guaranties that some information will not be lost. The information can be lost in the case when a document contains some elements which have no representation in a particular wiki syntax. Example: properties; tables  in lists; parameters of lists, paragraphs, and tables and so on...
- All elements managed by the WikiModel can be serialized/deserialized using XHTML with additional annotations (microformat-like annotations)

Some features of the CommonSyntax:
- It is a native syntax for the WikiModel. It provides full access to all features of the WikiModel.  All structures in the WikiModel can be serizlized/deszerialized in this syntax without any information lost
- It uses markup characters available in most (in ideal situation - in all) keyboard layouts (including Russian :-)). So you don't have to switch keyboard layouts to write text, tables, lists and headers. For example tables can be defined using pipe symbols ("|" - which is not available in many keyboard layouts) or the "::" sequence.
- If there is a choice then the most commonly used markups are used

The current version  of the WikiModel provides just an event-based interface  to  work with the structure of documents (like SAX for XML).
In previous versions of WIkiModel I had Document Object Model in which each structural element had its own object representation. In the current version an Object Model is not implemented (yet). I thought to create just a set of utility classes manipulating with the standard XML DOM. Example: the method WikiTable#setCellContent(int row, int column, String content) should create an XHTML table object, create the required number of cells and columns and put the given string content in this node. The same for all other structural elements (headers, lists, internal documents, properties, styles, macros...)


On 9/14/07, Vincent Massol <vincent@massol.net > wrote:
+1 to all that. So let me summarizes and rephrase to see if I have
understood :)

1) We have 4 types of objects:
* TextProcessors: take text and generate text
* Parsers: take text and generate an internal DOM format (pivot format)
* DomProcessors: take DOM and generate DOM
* Renderers: take DOM and generate anything (text, PDF, RTF, HTML,
XML, etc)

Yes.

2) Document contents are stored in the database in textual format in
the main xwiki syntax (whatever we decide it is - we could
standardize on creole for example)

It can be the "Common Syntax" for the reasons mentioned above :-). Creole syntax is one of the most restrictive syntaxes. And I tried to uses in the CommonSyntax as much markups of the Creole as possible.

An another possibility is to store directly in XML or in XHTML+microformat enhancements (for additional structural elements).
pro:
- it can be exported/imported directly and used by external applications which knows nothing about wikis; just a standard XML or XHTML
- this content can be transformed with XSLT processors directly without usage of the WikiModel
- it can be faster to parse XML than the CommonWiki syntax (I have no comparisons)
con:
- it is more difficult to work with diffs (but for diffs it is *better* to use WkiModel and to generate a specific wiki syntax; for example "Common syntax");
- it is not a "human readable" format; it is difficult to understand what you loads from the DB

3) Use case 1: Viewing a document
 

a) Get the doc from the DB --> text1 (xwiki text format)
b) Apply TextProcessors --> text2
c) Call XWikiParser --> DOM1 (transforms XWiki text syntax into an
internal DOM)
d) Apply DomProcessors --> DOM2
e) Call the required Renderer --> PDF, XML, HTML, RTF, text, etc

Yes.


4) Use case 2: Editing a document, assuming the user wants to use the
MediaWiki syntax for editing

a) Get the doc from the DB --> text1 (xwiki text format)
b) Call XWikiParser --> DOM1 (transforms XWiki text syntax into an
internal DOM)
c) Call MediaWikiRenderer --> text2 (text in MediaWiki format)
d) the user edits and hits save
e) MediaWikiParser --> DOM2 (transforms MediaWiki text syntax into
the internal DOM)
f) Call XWikiRenderer --> text" (transforms DOM into xwiki textual
format)
g) Save text3 in the database

Yes. (text1 and text3 can be XML, as I said above)


5) In practice this means the following classes:

* TextProcessorManager: to chain several text processors

Yes. But it can be just a composite processor implementing the same ProcessorManager interfaces.

* TextProcessor
   - VelocityTextProcessor
   - GroovyTextProcessor

Yes.

* WikiParser: Takes wiki syntax and generates a DOM in a XWiki-
specific format (independent of the different wiki syntaxes).
   - LegacyXWikiWikiParser
   - XWikiWikiParser (or simply use CreoleWikiParser if we want our
internal format to be Creole)
   - ConfluenceWikiParser
   - MediaWikiWikiParser
   - JSPWikiWikiParser
   - CreoleWikiParser
   - HTMLParser: I think all parsers above need to support HTML since
the wiki syntaxes can be mixed with HTML. So this HTMLParser is
probably a parent of the other parsers in some regard. Anyway we need
this one for the WYSIWYG editor which may need to transform HTML to
wiki syntax (so we may need a XWikiDomProcessor too to transform into
XWiki syntax). The alternative (much better) is to have the WYSIWYG
editor only use the internal XWiki-specific DOM format for all its
manipulations.

If you want, you can put HTML as a non-interpreted block ("verbatim blocks") and interpret it in the client code. But internally the WikiModel does not support "embedded" (X)HTML. The main reason: in this  case I loose control of the document structure. And this control is the main goal of the WikiModel.

* DomProcessorManager: to chain several DOM processors
* DomProcessor
   - Don't know yet what we're going to use this for. TOCDomProcessor
as you say above maybe.

DOMProcessor can be used to transform the original DOM object representing the document in the DB into a new (user and query-specific) DOM object which can contain new elements, generated dynamically. Now all dynamic page elements are interpreted as simple Velocity or Groovy scripts and they generate text documents which should be parsed using Radeox and transformed to the final HTML document. Using the DOM representation it is possible to interpret some nodes of this graph as Groovy scripts. In WikiModel they will correspond to Verbatim blocks which are opaque for WikiModel but they can be interpreted as scripts by the DomProcessor(s). And these "Groovy"-nodes can be executed and they will add new DOM elements to the DOM2. For example this approach can be used to generate search results.

The advantages of this approach:
- You can put your parsed document DOM1 in the cache, which will avoid you to to parse the document for each query. It is a slowest step in the page processing. Even if the current version of WikiModel is faster than before and it should be faster than Radeox processor.
- Your Groovy scripts will manipulate with normal java classes (DOM nodes) and it will produce DOM nodes and not a plain text. It seems especially interesting taking into account Groovy's Builders ( http://groovy.codehaus.org/Builders). It is enough to write a very simple builder (see http://groovy.codehaus.org/BuilderSupport ) generating DOM nodes and ... voila! Your Groovy node from a wiki page generates search results as DOM nodes!  These manipulations with DOM objects should be MUCH faster that process plain text for every request. And all following steps are fast as well - to generate an HTML page it is enough to visit all node with an "XHTMLVisitor".


BTW: do you need Velocity at all? Using only Groovy is much cleaner. It can be used as THE language of XWiki. It  can be used as a template *and* programming language at the same time. And if you *really* want it is possible to integrate Jasper (from Tomcat) engine to use it for pure templating. The code from Jetty (th e org.mortbay.jetty.jspc.plugin package) can be used as an example of integration with Jasper (see http://jetty.mortbay.org/xref/index.html).
In this case in templates it will be possible to use:
- JSP tag libraries (including standard ones)
- Multiple scripting languages (like javabeans, javascript, jpython, jruby, groovy,...)


* Renderer
   - XMLRenderer
   - HTMLRenderer
   - PDFRenderer
   - RTFRenderer
   - XWikiRenderer (or simply use CreoleRenderer if we want our
internal format to be Creole)
   - ConfluenceRenderer
   - MediaWikiRenderer
   - JSPWikiRenderer
   - CreoleRenderer

Yes. All these renderers should be written if you want to support all these syntaxes. I think that it should not be very difficult.

WDYT? Do I have it right? :)



Best regards,
Mikhail
 

Thanks
-Vincent

On Sep 13, 2007, at 6:37 PM, Stéphane Laurière wrote:

> Hi Vincent, hi everyone,
>
> We discussed the WikiModel integration with Mikhail this afternoon.
> Here
> is below our input.
>
> Vincent Massol wrote:
>> Hi,
>>
>> I've started working on designing the new Rendering/Parsing
>> components and API for XWiki. The implementation will be based on
>> WikiModel but we need some XWiki wrapping interfaces around it. Note
>>  that this is a prerequisite for the new WYSIWYG editor based on GWT
>>  (see http://www.xwiki.org/xwiki/bin/view/Design/
>> NewWysiwygEditorBasedOnGwt).
>>
>> I've updated http://www.xwiki.org/xwiki/bin/view/Design/
>> WikiModelIntegration with the information below, which I'm pasting
>> here so that we can have a discussion about it. I'll consolidate the
>>  results on that wiki page.
>>
>> Componentize the Parsing/Rendering APIs
>> ==================================
>>
>> We need 4 main components:
>>
>> * A Scripting component to manage scripting inside XWiki documents
>> and to evaluate them.
>
> On the topic of scripting we would like to propose a distinction
> between
> scripts that act on text and scripts that act on the DOM.
> Typically, the
> text rendering processing for flow would be the following, for say
> "text1":
>
> text1 =TextProcessor=> text2 =Parser=> dom1 =DomProcessor=> dom2
> => ...
>
> - the scripts contained in text1 are processed in the context of
> user1,
> this results into a new text: text2
> - the parser parses text2 and converts text2 to a DOM tree, dom1
> - dom1 is processed by scripts that work directly on the DOM (example:
> table of content generator), this results in dom2
> - dom2 is made to available as such or is converted to XML, HTML, PDF
> etc. depending on the user request
>
> TextProcessor and DomProcessor would have the following interfaces:
>
> TextProcessor
> - String execute(String content)
>
> DomProcessor
> - DOM execute(DOM content)
>
> That means we should have a syntax to distinguish between scripts that
> generate text content, and scripts that manipulate the DOM.
>
>>      * A Rendering component to manage rendering Wiki syntax into
>> HTML and other (PDF, RTF, etc)
>>      * A Wiki Parser component to offer a typed interface to XWiki
>> content so that it can be manipulated
>>      * A HTML Parser component (for the WYSIWYG editor)
>>
>> Different Syntaxes ===============
>>
>> Two possible solutions:
>>
>>     1. Have a WikiSyntax Object (A simple class with one property: a
>> combox box with different syntaxes: XWiki Legacy, Creole, MediaWiki,
>> Confluence, JSPWiki, etc) that users can attach to pages to tell the
>> Renderers what syntax is used. If no such object is attached then
>> it'll default to XWiki's default syntax (XWiki Legacy or Creole for
>> example).
>>     2. Have some special syntax, independent of the wiki syntaxes to
>> tell the Rendered that such block of content should be rendered with
>> that given syntax. Again there would be a default.
>>
>
> Here's our view regarding the syntax used in wiki edit mode: document
> requested for edition are available from the database in a serialized
> format, for instance XHTML. When entering into the edit action, the
> user
> indicates his preferred syntax. If the text of the requested document
> contains some blocks that are not handled by the chosen syntax, the
> user
> gets a warning (example: the document contains a table as a list item,
> and the user tries to edit the document using JSPWiki syntax). If not,
> WikiModel converts the serialized format into a DOM, the user edits
> the
> DOM and the WikiModel serializer serializes it back when the user
> saves it.
>
> Note that the DOM representation of wiki documents in the latest
> version
> of WikiModel is still pending.
>
>>
>> XWiki Interfaces
>> =============
>>
>>      * ScriptingEngineManager: Manages the different Scripting
>> Engines, calling them in turn.
>>      * ScriptingEngine
>>            o Method: evaluate(String content)
>>            o Implementation: VelocityScriptingEngine
>>            o Implementation: GroovyScriptingEngine
>>      * RenderingEngineManager: Manages the different Rendering
>> Engines, calling them in turn.
>>      * RenderingEngine
>>            o Method: render(String content)
>>            o Implementation: XWikiLegacyRenderingEngine (current
>> rendering engine)
>>            o Implementation: WikiModelRenderingEngine
>>      * Parser: content parsing
>>            o HTMLParser: parses HTML syntax
>>            o WikiParser: parses wiki syntax
>>            o Implementation: WikiModelHTMLParser
>>            o Implementation: WikiModelWikiParser
>>
>> Open Questions:
>>
>>      * Does WikiModel support a generic syntax for macros?
>
> WikiModel generates events for blocks that are not to be parsed
> (typically because they contain scripts).
>
> For example, in the WikiModel syntax currently called "CommonSyntax",
> this looks like the following:
> ==============
> {{{macro:mymacro (String parameters)
> dothis
> dothat
>
> }}}
>
>
> $mymacro(parameters)
> ==============
>
> For each syntax, macro blocks are identified as far as possible (we
> still have to check it's the case for all types of macro blocks inde
> indeed).
>
>
>>      * Is the Rendering also in charge of generating PDF, RTF,
>> XML, etc?
>>            o I think so, need to modify interfaces above to reflect
>> this.
>>      * The WikiParser needs to recognizes scripts since this is
>> needed for the WYSIWYG editor.
>
> the WikiModel parser recognizes scripts indeed.
>
>
> Mikhail and Stéphane
>
>>
>> Use cases
>> ========
>>
>>      * View page
>>            o ViewAction -- template ->
>> ScriptingEngineManager.evaluate
>> () -- wiki syntax -> RenderingEngineManager.render() ---> HTML, XML,
>> PDF, RTF, etc
>>      * Edit page in WYSIWYG editor
>>            o Uses the WikiParser to create a "DOM" of the page
>> content and to render it accordingly. NOTE: This is required since
>> rendering in the WYSIWYG editor is different from the final
>> rendering. For example, macros need to be shown in a special way to
>> make them visible, etc.
>>            o Changes done by the user are entered in HTML. Note: it
>> would be better to capture them so that they are entered in the
>> "DOM". Is that possible? If not, then the HTMLParser is used to
>> convert from HTML to Wiki Syntax but they're likely be some loss in
>> the conversion. The advantage is the ability to take any HTML content
>> and generate wiki syntax from it.
>>
>>
>> This is my very earlier thinking but I wanted to make it visible to
>> give everyone the change to 1) know what's happening and 2) suggest
>> ideas.
>>
>> I'll refine this in the coming days and post again on this thread.
>>

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