On 4 mars 08, at 13:27, Asiri Rathnayake wrote: Basically the idea is to make XWiki interoperable and addressable using the REST architectural style principles. At a high level of abstraction, yes the services will be provide the same functionalities of XMLRPC. But in a REST oriented solution the "interface" will be the one provided by HTTP (the 4 verbs), not a custom API like the one already present in the XMLRPC extension. There is a long debate about REST vs. SOAP (the comparison here is a bit wrong since REST is not a protocol), anyway REST and WS à la SOAP are two ways of doing WebServices that exploit rather opposite paradigms. So definitely I would say that we DO NOT want to do SOAP! :) To be concise the idea, following rest principles, is: 1) Give every XWiki resource an ID (i.e., an URI) 2) Make everything accessible through a uniform interface (i.e. HTTP or WebDAV) This implies: 1) Do some "resource" engineering in order to well define the URI space 2) Think about resource representations 3) Build the "business logic" to map the new way of accessing resources. Just an example for what it could look like. GET http://site/spaces -> gets the list of the available spaces POST http://site/spaces [SPACEINFO] -> create a new space DELETE htp://site/spaces/foo -> delete space foo PUT http://site/spaces/foo [SPACEINFO] -> Update space info (like description, etc.) etc. The trick here is that you have all the relevant things directly addressable and accessible through a uniform interface (i.e., HTTP or WebDAV). You will be able, for example, to say something like "GET http://site/space/page/object/field" and retrieve the value of the field of the object associated with a given page on a given space. Doing a PUT on that URI will set the value. Currently you have to do something like: XMLRPCClient .getSpace ("space").getPage("page").getObject("Object").getField("field"); The uniform interface (HTTP) allows you also to write the previous URI in a browser instead of compiling java code with brittle APIs :) An it would work :) Of course this is only the tip of the iceberg (and of the problems :)) Yes :) The foundation of RDF and all the semantic frameworks (à la semantic web) are the fact that "things" can be expressed and referenced through URI. In RDF, in fact, triples that establish relationships between thing are in the form SubjectURI PredicateURI [ObjectURI | Literal] To be more concrete I might say something like: person://fabiomancinelli http://ontology/fullname "Fabio Mancinelli" That basically states that my name is "Fabio Mancinelli", provided that person://fabiomancinelli is the URI that identifies the "physical person" that's me. Now, by exposing XWiki resources in a RESTful way we are basically exposing all the relevant XWiki "things" via a URI. We can use those URI for describing semantic relationships. So we could say something like http://site/space/page http://ontology/tag http://ontology/Technology http://site/space/page http://ontology/tag http://ontology/News In order to state that a given page has the Technology and News tags. Of course I've been very concise because it's not that easy and what I've described requires a lot of effort despite its simplicity. But if the engineering is done well this could result in a very powerful extension. It would be nice to send an email saying: "Hey Asiri look at the paragraph http://site/space/page/paragraph/1 and review it", then you do a "PUT on http://site/page/paragraph/1" and boom, the page will be updated reflecting the changes you did with respect to that paragraph. :) I hope that I've been clear. I know that's a not easy topic and it has a lot of nuances. Feel free to ask other questions. You are welcome. Cheers, Fabio

Fabio Mancinelli wrote: No, I would say that we'd rather have REST at this point as it has more direct benefits than SOAP, since REST does not need special tools to be used by simple users, while SOAP is mostly for machines. But I think that this project should not be done this way. It will mean that we'll have the application login in 4 places (struts, xmlrpc, gwt, reast). I'd rather we created a distinct application logic layer which can be used by all these communication interfaces (this is what they are, communication interfaces, and they should not contain logic). If we do this, then adding a SOAP protocol would be as simple as creating the listeners and the bridge to the application logic (2 weeks of work at most?). And it will be a little easier to update all the protocols at once. Also, this should be done in the new component-based architecture. How's that for a nice SoC project? -- Sergiu Dumitriu http://purl.org/net/sergiu/

On 4 mars 08, at 16:23, Sergiu Dumitriu wrote: Not sure of understanding what you say here. The XMLRPC login already uses, for example, the xwiki.getAuthService().authenticate method. Isn't this already the application logic layer you are talking about? Why do you need another? In the REST approach we would call this very same method in order to authenticate a request on a URI that is "protected", for example a PUT on a http://site/space/page. But maybe I have misunderstood something. Anyway, what is done in the "backend" doesn't prevent the fact that you must expose a URI space for addressing xwiki resources. This URI space engineering is the first step and doesn't involve implementation details [1]. Of course. But I was not talking about implementation details in my previous email. Actually I have a problem with another project proposal... I think there is some overlapping between the WebDAV and RESTful XWiki proposal because the description in http://dev.xwiki.org/xwiki/bin/view/Design/WebDAVService is exactly what I called "resource namespace engineering" in a previous message, and it's an integral part (actually it is the foundation) of the RESTful XWiki proposal. In fact for the RESTful XWiki we need a "view" of the XWiki system in order to make XWiki elements addressable through URIs that can be referenced by HTTP methods GET, PUT, POST, DELETE and, in case, by WebDAV methods PROPPATCH, PROPFIND, MKCOL, COPY, MOVE, LOCK, UNLOCK. Whenever a method is applicable, of course. So maybe the WebDAV and RESTful XWiki are actually the *same* proposal. WDYT? Cheers, Fabio [1] http://www.infoq.com/articles/rest-introduction

On 5 mars 08, at 10:11, Vincent Massol wrote: The problem here is that a REST solution and a SOAP one are incompatible. I am talking of pure-REST of course. REST talks about nouns, SOAP/ XMLRPC/etc. talk about verbs (the API). To me something like http://site/space/page?action=delete is NOT RESTful. So the "interface to the RESTful XWiki" (or more correctly the URI space) cannot be generated on the fly simply by exposing APIs encoded using URIs. This is not the RESTful XWiki I was talking about (actually it's not even REST). In fact, by doing this we would just introduce another XMLRPC API in disguise, and that's not interesting. Anyway, since there is already a misunderstanding at the possible mentoring meta-level :) maybe we should rule out this proposal and go for the WebDAV one that is already something that matches what I was originally proposing :) Cheers, Fabio

On 5 mars 08, at 11:07, Vincent Massol wrote: It's not just a problem of "uri syntax". It's a semantic problem. REST applied to the WEB prescribes that the HTTP uniform interface (and its semantics) should be used to access resources. Now if you have http://site/space/page/action/delete and you do a GET on it you are actually *deleting* a page. So basically you are subverting the semantics of the HTTP interface that says that GET is safe (doesn't have side effects on the resource state) and idempotent and returns a representation of the resource identified by the URI. This is valid for every "action" encoded in the URI (this is why I was saying that REST talks about nouns and not actions). Basically, by doing this (encoding an action in the URI), you "transfer" the semantics of the request from the HTTP method to the URI and that's not what REST says. Doing this kind of things is detrimental. Sometimes ago Google released this web-accelerator product that basically built a cache by performing GET requests in background. A sort of local crawler for speeding up the navigation. It has to be retired because people were implementing things in a non RESTful way (i.e., by subverting the semantics of HTTP through URIs). What happened is that the crawler, when was GETting some URI like the one you wrote, it was actually *modifying* the underlying resource. People were loosing data! So my proposal was in the direction of building a pure RESTful XWiki, as much as possible (i.e., one that comply with the HTTP semantics), not an hybrid thing (like many services that are already present: flickr, delicious, etc.). This is not interesting from my point of view and was not the spirit of my proposal. I understand, however, that this goal might be a bit "academic" and too research-oriented and might not be well suited for. But doing what you proposed, i.e. automatically generating a URI based API by simply encoding the backend API calls in URIs is not REST, and might do more harm than good. Indeed. Maybe it's going to be very complex. Being RESTful has tons of advantages but this comes at a price. A complete change of perspective. When designing RESTfully you stick to a fixed "client API" that is the uniform interface you choose, and on the Web is: class ClientAPI { Response GET(Request r); Response PUT(Request r); Response DELETE(Request r); Response POST(Request r); } With http://www.w3.org/Protocols/rfc2616/rfc2616.html as the "Javadoc" :) Then you start mapping what a POST or a GET or a DELETE on a given URI means in terms of your backend API (e.g., the XWiki API), in order to generate the Response. But the client has to see and use that API with the given semantics. I was saying that the WebDAV proposal was similar because in this case you would have this: class ClientAPI { /* HTTP */ Response GET(Request r); Response PUT(Request r); Response DELETE(Request r); Response POST(Request r); /* WebDAV */ Response PROPPATCH(Request r); Response PROPFIND(Request r); Response MKCOL(Request r); Response COPY(Request r); Response MOVE(Request r); Response LOCK(Request r); Response UNLOCK(Request r); } With http://www.w3.org/Protocols/rfc2616/rfc2616.html and http://www.webdav.org/specs/rfc2518.html as the corresponding "Javadocs". But still you have to design what can be GETted, PROPPATCHed, LOCKed, i.e., the URI space and what this means. To conclude, I am not saying that the automatic generation of URI mapping is bad (people are doing it most of the time and time) But from my point of view, the two proposals are totally different. This is the reason why I didn't agree with Sergiu: it's not just a question of implementation but rather a question of design. Anyway, nice discussion! This is really interesting and helps me to better understand these concepts that are not easy at all and sometimes very blurred :) Cheers, Fabio

Fabio Mancinelli wrote: No, we didn't quite disagree. I was not talking about the implementation, but about the design of the implementation. If we would write some restlets, then they would do what? Let's say we have the URL http://server/Space/Page/ and do a: - GET: duplicate some of the code in ViewAction - PUT: duplicate some of the code in SaveAction - DELETE: duplicate some of the code in DeleteAction - POST: duplicate some other code in SaveAction - HEAD: write some new code, as this is not done yet So I was saying that when designing the URLs, we should redesign the application logiC (and this is something you implied, too), but put it not in the restlets, but in another layer, so that it can be reused by other protocols. You do agree that we can't just design new URLs (or should we say IRIs?), without designing the logic behind them. Currently the logic is spread around all the platform. There is code in the Struts actions, in the XWiki giant, in the data model, in templates, in documents, in plugins (FileUpload, for example), so writing restlets that reuse this spread logic will be very inefficient: - search all around the code to see how to do something - duplicate code - copy the bugs along with the code - increase even more the mess And we can't just completely replace the servlets (and their URLs) with the new REST approach, as all the bookmarks and knowledge about the URLs would be broken, so people will not upgrade. So we either reimplement them using the new app logic layer, or write an URL rewrite engine that forwards to the new IRIs. -- Sergiu Dumitriu http://purl.org/net/sergiu/

On 5 mars 08, at 16:38, Sergiu Dumitriu wrote: After your message things are a more clear. I was just assuming that the "XWiki API" was already the layer you were talking about. But it is clearly not the case. And, of course, I totally agree on having a layer that factors things for maximum reuse in different contexts. So maybe we could rule out the RESTful XWiki, leave the WebDAV one (that on the user side is actually a super-set) and replace it with what Sergiu was proposing? WDYT? Cheers, Fabio

Fabio Mancinelli wrote: Sorry, my typo, I mean application LOGIC, not login. -- Sergiu Dumitriu http://purl.org/net/sergiu/

On 4 mars 08, at 14:02, Vincent Massol wrote: Hi Vincent, there is already an "XWiki Pure REST Api (compatible with GWT Apis, XML-RPC, SOAP)" but I don't understand where the corresponding project page is. Cheers, Fabio

On Mar 4, 2008, at 2:45 PM, Fabio Mancinelli wrote: Ludovic has already added it. You might want to edit it and add more info though. Thanks -Vincent