WWDC2000 Session 413

Transcript

Kind: captions Language: en good afternoon everyone can I ask you all a favor could you those of you who have large empty spaces next you could you please all kind of stand up and shuffle over a bit so a lot of people want to come in and see this and it's not nearly as much fun being in the overflow room thank you very much so people in the middle been very helpful here some of you on the edges can try and squeeze in a little bit one or two seats on the edge of makes a big difference helps people grab a seat and feel like they're part of the crowd here one big happy family right okay so we're talk about one of my favorite topics XML just to clarify some of you've been coming up and asking me about you know bug fix orders and engineering standards I am the product marketing manager okay I'm the marketing we need for web objects and development platforms I don't know the in-depth guts of all the engineering stuff Tony or the engineering teams can give you much better answers on that I handle all the warm fuzzy stuff so feel free to come ask me about those things but just direct your questions appropriately I'm also responsible for what we do with general development platforms including open source java and open standards which is what I'm very excited about this session on XML how many of you are doing things with XML today okay how do you think you're going to do stuff with XML in the next year or so okay so it's definitely coming down the pike we want to make sure that we have the best platform web objects Mac os10 open source as you know we does have already a sea-based XML parser that we've open sourced as part of the darwin project for mac OS 10 for people running into Mac OS 10 or core foundation api's we also have some very cool Java stuff integrated with web objects which is what Michael will be telling you about 9 now so introduce sorry Tim Johnson from web objects thank you very much thanks Ernie so what we're going to talk about today is web objects and XML and Ernie Ernie kind of stole my questions cuz everyone seems to be starting out with questions so I'm going to ask it again except slightly different I saw a number of hands go up to people doing XML stuff so just raise those hands again people doing XML today okay and those of you don't keep them up came up just for a second and those of you doing it with web objects okay so about half half the number of people okay thanks so what we're going to do is talk about XML today and we're going to start out with the basics of XML so most of you I think looking out there probably know the basics we just want to kind of cover that real quick now we're going to talk about the mechanics of XML with web objects now what what kind of facilities are web objects to deal with LEC's XML and kind of the typical scenarios I'm going to talk about encoding and decoding XML another way of saying is perhaps archiving and parsing reading and bending consuming and bending we're gonna talk about XML being used for server server communication there are lots of uses of XML but what we're going to kind of talk about here is really server to server that's really where web objects has a big strong role and can can do a lot and we're going to use content syndication kind of a very simplified version of that as an example to illustrate using XML with web objects so first of the basics of XML back with when the web started it was all about content the tagging was really to represent the different areas of content it wasn't about format what XML brings back to the table is is the content it really is all about the content and of course there are other ways ironically using XML to describe the format of formatting the XML over here but fundamentally it's about content it is a tag system much like HTML we have tags accepts a little bit stricter than HTML more akin to have sgml in its in its structured 'no sand rigidity does use plaintext as you're probably aware and the good thing of all this the good part of all this there really is pretty easy to learn the basics lots of books on XML and a lot of them don't even talk about programming at all they really treat it more like you know just kind of a structured ascii document and and how you how you can interact with this document and have this document represent meaningful and useful information and it is absolutely gaining a widespread acceptance for for data interchange which is really one of the reasons why we're going to focus a little bit on on that server-to-server communication so first a little sample XML file just so we all understand what we see looks we have tags here you can see the very top level is a model tag and everything else has been closed in that we clearly have tags and attributes the one thing I will point out for those who are kind of from the HTML arena is if we look at this first property list here where it says the third line down property name equals quantity at the very end the far right you'll see that that tag actually has a slash before the the end of it this is in an empty tag so this is something that that XML kind of brings to the table and something you don't haven't seen in your typical HTML document there's just a sample bit of XML so now let's talk about web objects and XML traditionally web objects is a server and it's used to vend information out and typically it's vending information out for webpages so there's this notion of a request and a response and in the server role the web object application takes in requests and sends out responses we start talking about server to server communication all of a sudden your web objects application server is also a client to some other location server so in a single app web office application may play the role of both the server and a client and so what web objects four five adds is a factoring out of the the parts of the requested response that were common and so we now have in web batteries four five introduced into the class hierarchy a whoa message and will request and will response our subclasses of low message so when you look at when you're looking for access to certain things that used to be in a request or response you might have to look in low message to actually get taxes those methods the good news of all this is that your request in your response have can now take on a different role they no longer have this predefined notion of I'm a server I'm a client in forw oftentimes you would have to do some some socket connections to go out and grab requests maybe you were in Objective C use NS strings little go grab this you you know go get me a string from this URL or or something like that well now we have a also have a structure in the in the mechanics of what objects to do HTTP connections and so we can actually have that client piece of an HTTP connection in your web apps application so what about is four or five ads that so it adds low message well requests or response or subclasses of that and we also have HTTP connection to do the encoding and decoding of the XML from the object world to the flat XML text world we've added will XML coder and will XML decoder these are two classes that really try to simplify the in and outbound XML data and all those those two classes are actually built on top of ibm's XML parser I will make a note that in what water is four or five to use these classes you actually have to be using Java as your programming language let's talk now about encoding when you encode you go from an object and you want to get out an XML file and we can actually do that with a single method so it's encode route objects with key that you passed an object and you pass it what XML tag you want associated with that top-level route and what you get back is an XML document this this XML coder will XML coder object can actually do this one method just kind of it magically works for any of the common types NS array and s dictionary Enterprise objects string number date and maybe a few others it's in the documentation I would definitely recommend that you take a look at the XML documentation that's in the what values four or five there's a PDF that describes all this as I'm going through spree reference so with this single method you can create these this XML representation of these objects if you have a data type that's not supported by that what you can do is you can write a custom method it's basically in code objects for key that will your past your past the object and your responsibility is to to return the XML representation of that object one of the things that you can this is all good and great okay I have a bunch of I have an EO and I just want to get an XML representation of that EO I just send this I send this object to this to the coder let it go to work the one thing to be aware of is that by default it'll it'll take that object and code it and then follow all the relationships all the related objects and encode them as well so the downside of this is that as you navigate relationships it goes to the next object so you have let's say you have an employee you archive the it codes the employee it then goes to the depart codes it but then there's an inverse relationship going back to employees so then it codes all the employees for that department so you can imagine that in a well connected object model everything your entire database gets encoded not exactly what you want in most situations so ways of avoiding this one is on your EO you can actually implement the custom encoder method and say which attributes in which relationships to actually encode and not you can also use a mapping file which I'm going to show in just a second or the other way is actually if it's possible you can actually turn off the class property of the inverse relationships it's not a class property it doesn't actually follow it to encode so let's take a look at this method the top one is kind of a single don't do any work throw in an object and get a get an XML out XML document out and it's basically you create a coder and you send it the encode route object for key message and the bottom one is using a mapping file you basically create a coder with the mapping file and then send that same message so what does a mapping file look like using XML we describe the mapping file it's this is actually the same one I showed earlier today what it says is what your entity name is and it says the texan alt tag to use and which attributes of that to actually encode with some flags to to deal with special cases now decoding again single method you can actually decode your object into your exit you can decode your XML into an object so you have this XML file and you want an object from it with the single method what you generally get back is either an array or a dictionary or an array of dictionaries and we're going to show this in the demo a little later you can also use a mapping file to specify how that encoding or decoding coding actually happens from the encoding standpoint you're typically going to do that use a mapping file in order to adhere to a certain DTD and decoding you're going to use that to basically map the XML someone's giving you into your your objects your enterprise objects and the attributes that are there unless you've convinced the other person to use the exact same names that you are you're using your Yeo's this is a side note for decoding and kind of excuse me parsing the documents you also have access the IBM parsers there so you can use the sax API to deal with that and the response object you can actually if it's an XML document you can actually ask it give me a Dom document from this from the request from the response content so there's HTTP connection kind of thing you get a document back if it's XML you can just ask that response object give me that thing as a Dom document and manipulate it with that API an example of of this is related links which goes out and uses the Netscape related links service on the web to you give it a website and it comes back with all the related sites that it's all done using mapping files so you can get a sense for that and it's a really good example of kind of all the little ins and outs and different ways of using the encoder and decoder one pitfall to avoid when you're decoding occasionally the decoder will look and if you have for say say three things that have name so you have three tags right after each other that are named or named Bob named Jane named Tim when you'll get us an array of three strings well there's only one what you're going to get is basically a single string back instead of an array of one size so there's a 1/4 list option in the mapping file that will always make it an array even if there's only one so I've seen that that bite a few customers so now let's go on to kind of uses of XML and the one we're going to focus on here is really server to server communication used often for data interchange and transferring and communicating between two applications going from the previous discussion you might actually use XML in this mechanism to the exchange snapshots even if someone thinks that's a flurry of activity but that's an example of some kind of thing you might you might use you also might use this for for remote method invocation there are a number of protocols out there XML RPC soap is another one that's that's gaining wide acceptance electronic data interchange is another example of server server just completing a purchase order or something like that content management it's generally a popular use for XML and dealing with putting content from one place to another there are number of people actually using this today with web objects there's a company down in Florida net Commerce Corp using all sorts of XML for content management there are a number of others that are that I'm sure here today doing similar kinds of things content syndication this is what we're going to talk about in just a second I have an article I'm a publisher I'm an author a site that has a bunch of authors creating content and I want to sell that or push that out to a number of different sites and these sites want to get kind of the top headline news so if I'm writers and I want all the I want to sell my content out we might use content syndication to push that out or for having them have them pull for that information and so their number of standards all the most of these are all based on on XML the bottom line is they're kind of two flows you either push the content to the subscriber or the subscriber periodically pulls for new content so in the push model a new article goes in and it gets pushed out to the servers and they're just sitting there waiting to accept it in the Polston scenario the subscriber periodically ask for requests do you have new articles and the publisher pushes out those new articles when asked this is actually the model that we're going to use for our little simple demonstration of putting this in action so what I would like to do is bring Michael Young on stage to give me a hand in creating a little Simple Syndication client and server so what we've done here is before we we started we created a direct web application director web is not a toy we create a simple direct web application here and what we're going to do is add syndication to this this is going to be our publisher so I'll use direct website add an article very simply so what we did was create a simple direct action class and called syndication and we're going to add a few methods to create this XML document on request so the first thing we want to do is kind of a general good coding a good programming style we want to create one coder object so whoa one whoa XML coder and we're going to save that as an Ivar on the top and we've got a bunch of code in the middle that goes out and given a certain client ID we'll fetch the articles that they have not seen yet have not received yet and those methods simply call this one method it's called encode article array so given an array of articles it's going to encode it into XML and return the response so we want to do is we have that coder we want to lazily initialize it so we'd want to initialize it all the you know in the beginning we want to wait till we actually need it and so we check if it's there yet and if it's not we go ahead and and create one the next thing we want to do is call that one method encode root object for key passing in the array of articles and giving it a key in this case the key we're going to give it is articles the next thing that we want to do is create a well response so we are going to be the vendor of this XML document and so we're going to create a well response that we're going to append this XML document to so we create our new low response and the first thing we're going to do is create the add into that response the XML kind of identifier for the actual document itself seriously the less than question mark XML version kind of thing here and since this is a hard one to remember we actually could just copy and paste this just to make sure we get it right so we now have the response we've added kind of this XML initial part and now we're going to go ahead and and append that content to the response and this is our XML string we did with the one line in code root object for key and finally what we want to do is set the mime type so that the receiver of this will actually get the understand it as an XML document as opposed to trying to interpret it as an HTML document and finally see that we return the response so we're going to do is go ahead and build this and if someone we haven't made any typos compile we're going to go ahead and run it and if we could switch to machine for I've machine five sorry so if we bring up our browser now what I'm going to do is access that site that application as if I'm a Content subscriber a syndication subscriber so this is pretending I just want looking for all the XML the XML version of the doc of the article listing of all the messages so I have that bookmarked here and what we get now is produced by that direct web application with that little direct action class we'll add in we now have an array of articles in this case three articles you see our XML version up here and each article has inside it published state the text and you'll notice that it also has references to in this case because we encoded AOS it has relationships in this case it to one so on the when we get to the building the server that sorry the syndication client the subscriber because we have two web obvious applications we're going to take advantage of that and we're actually going to get a yo generic records back on the other side so we'll be able to do all of our key value coding very easily so we have that now what we want to do is build so if we switch back to machine for now we want to do is build that syndication client and add the decoding so take this XML string that we just saw and make objects out of it what does that take and so we have is we have a little application that's really just designed to kind of show news articles and again the first thing we want to do is create an Ivar for the decoder just kind of have that around and reuse it creating a decoder or an encoder is a little bit of a heavyweight operation we don't want to do that for every single request and now we want to do is create use that web objects as a client functionality that's been added and create a whoa HTTP connection object and what this takes is a host and a port number and then we're going to go through the process of sending a request over the line so we're we could start chanting faster faster faster so now what we're going to do is take that HTTP connection that we have and we're actually going to send a request through that connection and the request we send it's actually going to be a whoa request object so again you get to use the same classes you've been using before the difference is you're using them in the the opposite manner that you have been accustomed to in this case we actually create well requests and get back well responses as opposed to the traditional role of getting requests and making responses and after we send that request what we want to do is actually we have the request now we want to do is pull the response out of that out of that connection request so we're going to read the response into a response object and again do that lazy initialization since we haven't want to make sure we actually have a decoder already and if we don't we need to create one so at this point we have the XML document in a will request a wrote will response and we have a decoder so now we get to call that one method decode route object and decode route object given this this NS data will give us our objects back and in this particular case what we're getting back every time is an array an array of articles it may be an empty array if there were no new articles but we're always going to get back an array so we decode it and we have these new articles now what we want to do is simply add these articles to an existing array of articles that we have so the very first time we run the application it goes out and fetches all the articles and then every other time it requests them if there are new ones we'll simply add that to the list of available articles we have now there are a whole bunch of we very simply made this very simple we simplified the problem and in fact we're going to ask for new articles on every request that comes into the application we're doing this pretty much entirely from a demo perspective because having a time we're sitting there you know we sit even longer than we have been watching waiting for Michael to type faster faster faster faster okay so we're done so we're going to go ahead and run this application so it's built and we're going to run it now and what we're going to do at this point is bring up both we're going to split the screen so for the overflow room I apologize if it gets a little difficult to follow we're going to have is on the screen to my left your right we're going to have the servers and we have both servers running there and on the other screen we're going to have the browser so if you want to switch so we have the both of them looking okay so what I'm going to do is simply access this this got this site so what we have here is the three articles so when I when we did that when I first accessed it it went across to the subscriber ask the publisher give me your articles and if you can highlight Michael that the XML oh sorry I got ahead of myself we're not logging at this point what I'm going to do now is we got with those three articles back I asked for all the messages there are currently three messages in the system so what we're going to do now is add a message to the system so I'm going to go back to the I'm going to go to the director web version of the application this is the publisher now and I'm just going to create a new article so I'm going to create a new article and say Larry Ellison Sue's San Jose you want to land is jet at night okay and the publication date for this one we're going to make it May what's today's date 18th May 18th mm and this has to do with airports and I'm the author here so I'll go ahead and I'm going to save it it's going to go into the database but no syndication will happen immediately all right so that article is saved now what I'm going to do is I'm just going to click on a link here any link will cause a request to the application which is going to cause like I said every request that comes in to the news site will go off from the subscriber to the publisher and get the new articles and so what we'll see is when I click on this will see the to send the XML messages back and forth and then it'll be added to this page here so when I click on this it goes across and when we see at the bottom we see at the top is the actual XML that got created again that yo generic record and at the bottom you see that we inserted one new article on the bottom half and it's like if I click on this you'll see that we constantly just get 0 new articles added to the system so we've used the client capabilities in our web obvious application HTTP connection to send requests out get back XML content and turn them into objects that are rendered in our web pages and on the publisher I'd we've gone to the database taking our AOS and encoded them in XML and sent them out in this case based on a direct action clearly there's lots of stuff clearly there's lots of stuff you want it you know you want a polling mechanism you know to do it on a timer you want security between all this but these were we're really to highlight those api's that you're going to want to be familiar with to do these things so thank you Michael and Michael view back for QA a little bit what do I do now let's switch back to the slides and that's using whoa XML coder and will XML decoder to do that XML but there is another way and it may be so how many people have actually used well XML coder or decoder out there a couple alright so how many people have done XML web objects basically using the component model just building a component in generating XML okay we have a couple so a whole lot of hands went up earlier that you're doing web objects and XML stuff I'm missing something what else have you used object space the XML okay so you're just taking your objects and created XML using other libraries solution okay so using it using other things to create your XML okay well besides the will XML coder and decoder you can use the component model the component model basically says to date we've been using components as part of pages to generate a HTML document these documents happen to be tagged so why can't we just make these documents of an XML type and the answer is you can easily do that and we're going to have a demo of an example of that coming up real soon but web objects itself actually uses this method my understanding just to make sure I'm right is the directive Java client actually uses this to create those XML part of the XML that goes out to the Java client application there are components that are generating this XML so you can actually use what Bobby's builder to put XML do the petitions simply inserting the tags using low generic container will generic element or we can also use a new class a new component that was added in four five I believe called whoa XML node it's in the well extensions framework and it really is probably the easiest way to learn just you want to create an XML document you can create and build or connect up some generic elements generic containers bind them to things and you should be able to create XML very quickly without understanding kind of the other api's and ins and outs of encoding and decoding because you really are just creating a character string going out and but but you don't want to forget to set the header to the text XML content type so you want to set your mind header the mime content-type so what I do now is bring on Ron Luce saying who you saw earlier today doing smile it was really focusing there on the client side putting using smiles make quick time your browser or not use your browser and you have QuickTime to your UI we're going have what Ron's gonna talk about now is how he did that using generic element generic container and will XML there okay so how many of you were here for the session earlier this morning whoa hello okay so you guys did you guys like that okay all right thank you so now you're probably wondering though so exactly how did I come how did I build the framework what it what does it really look like okay here's the source for the framework I've got a whole bunch of web components and they pretty much map directly to all the elements that are in the smile the smile spec each of the elements like the document the media objects everything has its own component and I even have a sort of a inheritance model here that all inherits from smile element simple thing as Tim had said you want to remember those at the mimetype what I do in my framework though is for the smile document I actually set the mime type for application smile since this is smile specifically versus generic XML each of these elements has a couple of things in them the main the very important one the one that you guys all saw this morning there's the smile media object I've got some logic in here for actually generating the source and the the href tag the href attribute that goes along with the tag a whole lot of other things that are in the smile spec that aren't often used but for completeness I added them here as well so all of these though are generated from little components and most of them only contain Jews let's try this one most of them only contain this this is all that I did I've got component content so that you can nest things and then the actual media object that has all of these bindings all these beautiful bind goals so you can just bind so by doing this you can lay them out in Wahb the way you would layout HTML elements that you normally would so to see an example of that here's the application that i showed earlier and the video page this is actually what it looks like beautiful smile elements Billy that you can bind all of your logic to you can set the mime type for any of the media that you're sending out four-foot smile media objects and there's also so one thing with with all these low components web objects really wants to know what bindings are going to be in there beforehand so that's why I have all these very very long list of variables and so my objects now what if you've got some things that you don't really know ahead of time that in my framework I don't really know ahead of time what you people who would be it who would build applications using this would use and as attributes in your smile tags so I left one thing in here a other tag string so this lets me add random things to to any of the tags that get that get generated for my smile documents so in my application here there are some extensions to smile that were added by quick time so quick time player can understand a couple more tags and one of them is the key T autoplay KP time slider and the key T next values if I can run this real quick so I can run this on a different port real quick and switch over to box box five so it's got so we can go and take a look at the actual source here and let's choose actually why don't we Sherlock for it let's do that that's another thing so Sherlock okay use of XML here still will components on my app side I've described what my application is going to send back to Sherlock once it's found something how it's going to be formatted how all the results are formatted it's formatted here as XML like so this truly is an XML but the formatting is the same what what's important though is I can use the lo XML node to generate the the tags the exactly these relevance and result those items so I can just change one thing we'll take a look at all the songs in my app so let's try rock songs well we'll try also well well we'll skip the show-off part okay now I've got a direct action in my app that will give me pop rock music we're supposed to give me pop rock music okay well I'll have to skip that can we go back to number two please no wonder seems to be something using my open base connection alright well the main thing I wanted to show you though is what it looks like once we've actually generated all the all of the once we've bound all the tags to two values in our logic it looks basically like this except all the web objects tags really are changed you've seen this before it looks just like your HTML would and that's kind of the beauty of it right you can still use wob to generate something that isn't really what you're used to generating with web objects right you've got instead of HTML you're generating xml and you can use stuff beyond just component content and web components you can use the whoa xml node my framework for generating sherlock information got a sub project here called search me and this is what the tags look like in here you can see here I've got little XML node and the cool thing so I've mixed lots and I'll node with low repetitions and low strings and low links little hyperlink this is another advantage so if instead of having to go through and concentrate on using the map encoder and generating all the extra stuff that you would need to talk to Sherlock go to QuickTime you just build it in what in Wahb and it all kind of just works kind of a nice thing about it so I suggest that everyone try this out it's beautiful thing yeah thanks Ron so you have two opportunities you can use will XML code or decoder if you're going to be vending and consuming and trying to go both directions perhaps it's worth learning that if you just want to be vending XML out to other sites or other users or other applications then the component model makes a lot of sense because it's a really natural fit for what you've probably been doing with with generating HTML applications so web object and XML in summary it can be both a vendor and a consumer of XML we've added facilities to deal with the client side of an HTTP connection as well as both consuming and vending the XML itself easy encoding and decoding encoding component model or will XML coder decoding will XML decoder as well as other api's mapping files if you need DTD adherence both in and out and it's actually used within the web live application web objects product itself in a number of number of different ways direct Java client being just just one of them and it is used today by the number of hands by a number of developers out there already so I encourage you to go and start to to create XML stuff and and vend it to the world so with that like to bring Michael and run back up to answer any questions and Ernie any questions that you might have about XML above it so it began for Tim in the gang you