Book HomeCascading Style Sheets: The Definitive GuideSearch this book Tuesday 03rd of March 2015 04:03:40 AM The 2nd category of Java applications called Java Application Servers (or app servers) and they make good use of XML. Unlike client side graphical Java apps (from the previous section) which are very standalone in their operations, app servers tie many different networked software components together in order to provide information from multiple sources to a set of client side Java apps or web browsers (maybe even running on different devices). This is shown in Figure 2. An app server is actually a conglomeration of several distributed and client/server software systems. So when you write an app server, you are actually writing many different software systems which are all networked to work together, to process information that comes from various sources, and distribute this information to a set of client apps (that you also have to write) running on different devices and platforms.

How can XML help app servers do their work? As you can see in Figure 2, in order for the app server to harvest information from such a rich variety of sources, there must be some common ground between all of these sources (each of which might be running on a different hardware and software system). This common ground is the information which flows throughout the entire system, regardless of what source the information comes from. CORBA is an example of tying disparate systems together based on the interfaces that certain remote objects implement. XML does the same thing for data. It allows these disparate systems to share information in a medium that consists only of pure information (and the structural relationships that exist inside of that information). By taking the lowest common denominator approach by using plain text to encode data, XML allows these systems to talk with each other without requiring any special binary information format converters or other service layers to translate between binary formats (for encoding data). Also, since HTTP already supports transmission of plain text, it is completely natural to move XML around using the Hyper Text Transfer Protocol through firewalls and disparate networks. This is shown in Figure 3. XML can be transmitted between systems using one of the most prevalent protocols in use today, Hypertext Transfer Protocol or HTTP 1.1 (which is the protocol of the web).

App server developers are not restricted to using HTTP, they can transmit and recieve XML information using simple remote CORBA objects and RMI objects. The key is that by using XML, it makes these remote services or objects easier to build. And, by sticking with XML, any one of these technologies can be used in your design of your app server. You can use whatever technology is most appropriate to getting the job done, knowing that all the information flows as XML and can be processed by any part of the system. The reason Java object serialization did not achieve this is because it encodes object data to a binary format that is dependent on too many things (like the JVM version, and the existence of classes when things are deserialized, etc). XML is not limited by any of these restrictions (or problems), which makes it much easier to create systems that allow XML information to flow between different subsystems. Also by relying only on the data, large portions of the system can be replaced with better or different implementations for future-readiness.

App servers traditionally give their client apps access to information in remote databases, remote file systems, remote object repositories, remote web resources, and even other app servers. All these information sources don't even need to reside on the machine that hosts the app server. These remote resources may be on other machines on the Intranet or the Internet. Using Java and XML, RMI, JDBC, CORBA, JNDI, Servlet and Swing, you can create app servers that can integrate all kinds of remote and local information resources, and client apps that allow you to remotely or locally access this information from the app server.


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elements is something almost every author will want to use, probably quite often. Used properly, colors can really strengthen the presentation of a document. Once you've decided how you plan to use color, you have to decide how you'll apply it, since some approaches will require the use of classes as well as simple element selectors.

As an example, let's say you have a design where all H1 elements should be green, most H2 elements should be blue, and all hyperlinks

11.2.7. Preserving Boldness

Here'sa similar trick that helps work around a bug in most versions ofNavigator 4. In situations where font-weight:normal has been set on an element, this value willbe inherited by all the descendants of the element. That's asit should be, of course, but Navigator takes it one step too far.

<P STYLE="color: gray;">This paragraph has a gray foreground.</P>
<P>This paragraph has the default foreground.</P>
Figure 6-1

Figure 6-1. Declared color versus default color

TIP

In Figure 6-1, the default foreground color is black. That doesn't have to be the case, since users might have set their browsers (or other user agents) to use different foreground (text) colors. If the default text were set to green, the second paragraph in the preceding example would be green, not black -- but the first paragraph would still be gray.outside, then it is placed in the margin of the list-item element. The exact behavior in this circumstance is not defined in CSS.

list-style-typeIE4 Y/Y IE5 Y/Y NN4 Y/P Op3 Y/-

This is used to declare the type of bullet numbering system to be used in either an unordered or ordered list, depending on the value specified. This property applies to elements with a display value of list-item.

This would cause the element to appear wherever it normally would,despite the fact that the ancestor (and possibly the siblings) isinvisible. In order to do so, you would need to explicitly declarethe descendant element to be visible, sincevisibility is inherited. Thus:

P.clear {visibility: hidden;}P.clear EM {visibility: visible;}

As for visbility: collapse,this value is used in CSS table rendering, which isn't covered