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From "Tom Klaasen (TeleRelay)" <tom.klaa...@telerelay.com>
Subject RE: [RT] Flowmaps revisited
Date Wed, 10 Oct 2001 09:07:15 GMT
Hi,

I'm impressed... This would even solve problems I've got now with Struts
(which is concentrating solely on webapp development)

One point though: you should work out point "(6): form submits" some
more . Form validation is *the* PITA in webapp development, not in the
least because the user wants to see some feedback about what he did
wrong. I don't see that in your solution (but then again, I still have
to see the first webapp framework that solves this properly. My hopes go
to XForms, because I've done some pretty nice things with that).

On a second level, have you thought about multi-page forms (one form is
filled out in multiple stages. There _are_ situations where you want to
do that) and multi-form pages (several forms on one page, and depending
on which form you press "submit" on, you go to a different location)?

Keep up the nice work.

tomK



> -----Original Message-----
> From: Daniela Gehle [mailto:d.gehle@levigo.de] 
> Sent: dinsdag 9 oktober 2001 16:48
> To: cocoon-dev@xml.apache.org
> Subject: [RT] Flowmaps revisited
> 
> 
> Dear Cocooners,
> 
> I've been following your discussions concerning the Flowmap topic with
> high interest, as our company is working on a web application showing
> exactly the same problems that could be solved by some kind of Flowmap
> or Transition Map (as I prefer to call it to avoid confusion with the
> ongoing Flowmap proposals).  We've been reading and discussing your
> proposed approaches carefully and found valuable inspiration in it.
> (Although some parts of your proposals are still covered with 
> mist, for
> example the usage of filters in Berin's proposal. Maybe 
> someone else can
> enlighten us. :-)
> 
> Resulting from these considerations we envision a slightly 
> different and
> "lighter", but not less powerful way to implement flow 
> control in Cocoon
> 2, which I would like to present you herein.
> 
> This approach is "lighter" in the sense that it can easily be 
> integrated
> into the current Cocoon 2 framework using the actors concept. Once the
> Cocoon Sitemap implementation will change from compiled to 
> interpreted,
> this approach can easily be adapted and integrated into the 
> new Sitemap
> concept. But for now all we want is a generalized 
> implementation without
> any changes affecting the Cocoon framework itself.
> 
> Of course we would like to contribute the implementation of this
> Transition Map approach to the Cocoon project, so please let me know
> what you think about it, if we misunderstood some of your points or if
> we are missing any important details. The proposal itself is not
> entirely fixed yet (and of course not yet coded as well :-), so you
> still have the opportunity to influence the design we propose, to make
> it perfectly fit into the Cocoon framework.
> 
> Ok, fastened your seat belts? - So let's start with the explanation:
> 
> ---------------------------------------------------
> Reminder: Pages, navigation and flow.
> ---------------------------------------------------
> One of our web applications requires the user to step through a number
> of pages in a controlled sequence (or "flow"). Each of these pages is
> accompanied by background "actions" performed by Java classes. These
> actions concern data generation as well as data processing. 
> From each of
> these pages just a very small, context-dependant subset of other pages
> is accessible, and only these transitions should be displayed to the
> user.  What makes these transitions even more complicated, is 
> that some
> of them require not just the target URL but additional data 
> that will be
> processed by the underlying program logic.
> 
> This is very much in contrast to most of the common web applications
> where you have some kind of   general navigation menu accessible from
> each of the pages and provide the same navigational links for 
> all of the
> pages.
> 
> Therefore we can distinguish two different types of navigation:
> 
> - navigation as a way to consistently structure and group resources
> (mostly in a hierarchical manner) and make them accessible 
> for the user
> in a fashionable way (we could call this type of navigation "static
> navigation"), and
> 
> - navigation that refers to states in a flow and grants access to a
> subset of pages that are part of a flow. We call this type of 
> navigation
> "flow navigation" from now on.
> 
> Static navigation is a pretty simple issue, so we will concentrate on
> flow navigation in this article. As a special aspect of the 
> flow control
> presented here, the approach provides a mechanism to generate these
> "flow navigation" elements automatically from the state description in
> the Transition Map. As far as I know, this is a topic that has never
> been addressed on the Cocoon list before. 
> 
> I don't want to confuse you - so I will touch this mechanism only
> marginally within this presentation, but in fact it is an important
> requirement that had fundamental influence on the presented design. If
> you are interested, let me know, and I will feed you with additional
> details.
> 
> ---------------------------------------------------
> What issues do we cover?
> ---------------------------------------------------
> Now that we know the rough picture it is time to look a little bit
> closer at what requirements have to be met exactly. This flow handling
> approach covers not only flow control itself but some 
> additional aspects
> as well:
> 
> (1) Controlling the flow (i.e. state transitions) of the application.
> (2) Separation of data processing ("control" aspect of the 
> MVC pattern)
> and data generation ("view" aspect of the MVC pattern).
> (3) User authentication and authorization.
> (4) Jumping to any visible state in the middle of the flow in 
> one hop. 
> (5) Automatic generation of "flow navigation" elements for each page.
> (6) Handle form submits.
> (7) Support generation of forms.
> 
> We will see how all this works together later. 
> 
> --------------------------------------------------------
> Sample application
> --------------------------------------------------------
> The problem description is borrowed from the concept of finite state
> machines and relies on a formal description of states and transitions.
> Please note that this is the main difference to the previous
> propositions on this list - we do not just concentrate on the states,
> but on transitions as well. Each transition requires a 
> particular set of
> parameters tied to the transition. These parameters are used 
> to generate
> flow navigation elements and forms.
> 
> Let me explain this with an example. Assume a flow representing an
> archive searching application requiring user authentication. For
> example, think of a newspaper article archive containing articles to
> several topics where autorized journalists are allowed to 
> drop queries.
> The page sequence that is crossed  performing a query might look like
> this:
> 
> login -> topic-selection -> search-form -> result-list ->
> article-display
> 
> The main processing direction is forward, but a backward navigation to
> any of the previous pages has to be supported as well. If you are
> currently looking at a newspaper article (article-display page), you
> might want to jump to the page where you can change the 
> selection of the
> topic (topic-selection page). Or you might want to change 
> your password
> from any of the pages - this means that access to a "change-password"
> page must be possible from every page.
> 
> This shows us that the flow is NOT just a simple sequence of pages
> processed in a row, but of a much more complex structure (which is not
> really easy to draw in ASCII graphics and therefore be 
> omitted here :-). 
> 
> Moreover, we have been cheating a little bit so far. The flow consists
> not only of pages - representing visible states of the system
> (accessible via an URL) - but also of hidden states where system
> operations are performed (like data verification or query processing).
> These hidden states can lead to visible states or to other hidden
> states.
> 
> Therefore, the login sequence of the above mentioned page flow should
> better be written like this:
> 
> login --(AUTH)--> [check-login] --(AUTH-OK)--> topic-selection ->..
> login <--(AUTH-NOT-OK)--|   
> 
> Please note that in this notation the transitions themselves 
> have unique
> names like (AUTH) or (AUTH-OK), and the hidden state [check-login] is
> marked with square brackets to illustrate the difference to   visible
> states. As its name proposes, the [check-login] state verifies and
> processes the data entered in the login form on the login page.
> 
> Another important point is that the transitions are transporting data
> from one state to another. The (AUTH) transition, for example, carries
> fields like username="paul" and password="foo". These fields will be
> evaluated by the subsequent state.
> 
> Now we can put together a description of all states and all 
> transitions
> in a Transition Map:
> 
> --------------------------------------------------------
> The Transition Map
> --------------------------------------------------------
> <flow start="login" name="search-archive">
> <transitions>
>   <transition name="AUTH" target-state="check-login">
>     <parameters>
>       <parameter name="username" xpath="/environment/user"/>
>       <parameter name="password" xpath="/environment/pass"/>
>     </parameters>
>   </transition>
>   <transition name="AUTH-OK" target-state="topic-selection"/>
>   <transition name="AUTH-NOT-OK"  target-state="login"/>
>   <transition name="SELECTTOPIC" target-state="find-topic">
>     <parameters>
>       <parameter name="topic" xpath="/topics/topic"/>
>     </parameters>
>   </transition>
>   <transition name="LOGOUT" target-state="perform-logout"/>
>    ...
> </transitions>
> <states>
>   <state name="login" resource="*/login">
>     <if event="AUTH" transition="AUTH"/>
>     <if event="CHANGEPASS" transition="CHANGEPASS"/>
>   </state>
>   <state name="check-login">
>     <act type="LoginAction"/>
>     <if event="OK" transition="AUTH-OK"/>
>     <if event="ERROR" transition="AUTH-NOT-OK"/>
>   </state>
>   <state name="topic-selection" resource="*/topic-selection">
>     <if event="LOGOUT" transition="LOGOUT"/>
>     <if event="SELECT" transition="SELECTTOPIC"/>
>   </state>
>   <state name="perform-logout">
>     <act type="LoginAction"/>
>     <if event="OK" transition="LOGOUT-OK"/>
>     <if event="ERROR" transition="LOGOUT-NOT-OK"/>
>   </state>
>    ...
> </states>
> </flow>
> 
> A Transition Map can contain several flow definitions, each of them
> carrying a unique name and being responsible for a different 
> functional
> unit (<flow start="..." name="...">).
> 
> The first part of each flow definition consists of the 
> definition of all
> transitions (<transitions> ... </transitions>). Each transition is
> described by a unique name, a target state and the parameters that are
> required for this transition. These parameters are NOT 
> necessary for the
> flow control itself, but they are for form handling and automatic
> generation of flow navigation elements. They result either 
> from filling
> form fields or represent environmental data provided by the data
> generation classes. The latter can be evaluated automatically 
> by using a
> specialized "FlowNavigation" transformer, but I don't want to mix up
> things here, so I'm concealing the details of this 
> transformer for now.
> 
> To describe the flow as a whole we do not just need the 
> transitions but
> also information about the states and by which transitions they are
> connected. The state descriptions (<state>...</state>) distinguish
> between visible and hidden states. Visible states can be reached by
> requesting a specific URL - hidden states cannot.  Visible 
> states carry
> the URL resource they are mapped to in the resource parameter of the
> <state> element; hidden states carry information about the 
> handler that
> is executed when entering the state. These handlers can be implemented
> as actors. It might be possible for a visible state to 
> contain a handler
> as well, but this is not recommended, because then the clean 
> separation
> of visible and hidden states would be broken. 
> 
> The decision which of the possible transitions to follow at a specific
> point is done by evaluating the transition event parameters. These
> parameters are either URL parameters (in the case of a 
> visible state) or
> result parameters of an action (in the case of a hidden state). Event
> parameters are written in Capitals in order easily 
> distinguish them from
> ordinary parameters. 
> 
> --------------------------------------------------------
> Sitemap configuration: the FlowHandlerAction
> --------------------------------------------------------
> In order to control the flow and the state transitions there is a
> FlowHandlerAction hooked up in the Sitemap. More precisely, the
> FlowHandlerAction will be performed for each URL that is 
> representing a
> (visible) state in the flow.  The FlowHandlerAction has to be fed with
> the name of the flow for each pattern match within a flow. 
> 
> The Sitemap contains something like
> 
> <map:match pattern="in-the-flow/*">
>   <map:act type="FlowHandler">
>     <map:parameter name="search-archive"/>
>   </map:act>
>   <map:act type="AuthenticationAction">
>     <map:redirect-to uri="in-the-flow/login"/>
>   </map:act>
>   <map:generate type="saxlet" src="templates/{1}.xml"/>
>   <map:transform src="styles/{1}.xsl"/>
>   <map:serialize/>
> </map:match>
> 
> The Transition Map file itself will be specified within the definition
> section of the FlowHandlerAction:
> 
> <map:actions>
>   <map:action name="FlowHandler" src="org.bar.foo.FlowHandlerAction">
>     <map-file>transitionmap.xmap</map-file>
>   </map:action>
> </map:actions>
> 
> --------------------------------------------------------
> Are all the promised features there? 
> --------------------------------------------------------
> (1) Controlling the flow (i.e. state transitions) of the 
> application? -
> Yes. 
> 
> (2) Separation of data processing ("control" aspect of the 
> MVC pattern)
> and data generation ("view" aspect of the MVC pattern)? 
> 
> Yes. Control is performed by the handlers of the hidden states, data
> generation is performed by the specific Generator 
> (ServerPagesGenerator,
> SAXLet Generator,...) for each page representing a visible state.
> 
> (3) User authentication and authorization? 
> 
> Yes. Except for the login process itself which is performed by the
> LoginAction Handler of the "check-login" state, user 
> authentication and
> authorization are located in the AuthenticationAction used in the
> Sitemap. Please note that this is one of the main differences 
> to Berin's
> proposal, were an authorization mechanism was part of the flowmap
> itself. We decided to put the authentication and authorization aspects
> apart, because not all applications rely on the same consistent
> authentication/authorization mechanism. Therefore, in order to be open
> to any authentication/authorization requirements, it seemed 
> to make more
> sense to  place them in actors called from within the Sitemap or the
> Transition Map. Of course, a combination of both approaches 
> is perfectly
> possible.
> 
> (4) Jumping to any visible state in the middle of the flow in 
> one hop? 
> 
> Yes. This is possible, provided that the necessary ordinary and event
> parameters for the march along the transitions leading to the desired
> target state are passed along with the HTTP request. As long as the
> required parameters for the transitions between the states 
> are contained
> in the URL, the state machine will jump from state to state without
> bothering the user with displaying pages belonging to intermediate
> states. 
> For example: If you want to jump to the state "search-form" without
> crossing the "login" page, you can enter the URL:
> http://foo.bar/in-the-flow/login?username=Paul&password=foo&AU
> TH=true&topic=squirrels&SELECT=true.
> Starting from the "login" state the subsequent states "check-login",
> "topic-selection" and "find-topic" are automatically crossed, 
> leading to
> the target state "search-form" (and displaying the 
> "search-form" page to
> the user). 
> 
> (5) Automatic generation of "flow navigation" elements for each page? 
> 
> Yes. This task will be performed by a specialized FlowNavigation
> transformer using the xpath attributes of the transition 
> descriptions in
> the  Transition Map, matching them against XML elements of 
> the generated
> data and inserting generic "flow navigation" controls in the XML data
> that is being processed.
> 
> (6) Handle form submits? 
> 
> Yes. Default target of a form submit is always the current 
> page (=state)
> itself. The FlowHandlerAction checks if there's an event parameter
> triggering a transition leading to another state (according 
> to the state
> and transition description in the Transition Map) or if there is no
> matching event parameter and the page itself has to be generated.
> 
> (7) Support generation of forms? 
> 
> Yes, this is possible in combination with flows, but not implemented
> yet. Using a form descriptor similar to the <parameters> 
> element of the
> transition description in the Transition Map, forms can be 
> generated in
> a unified way, with the default form submit target being the current
> page.
> 
> -------------------------------------------------------------
> How does this proposal fit into the future plans for Cocoon?
> -------------------------------------------------------------
> That's a point pretty hard to answer for me, because I cannot sneak in
> the heads of the Cocoon front row developers. All I could do is point
> out the aspects we've been considering. Now it's your turn, 
> please throw
> your stones. ;-)
> 
> Thanks,
> Dani
> 
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