Welcome!

Agile Computing Authors: Mehdi Daoudi, Yeshim Deniz, Jyoti Bansal, Elizabeth White, William Schmarzo

Related Topics: Industrial IoT

Industrial IoT: Article

XHTML: XML On The Client Side

XHTML: XML On The Client Side

The XML developer doesn't have to be convinced of XML's strength. You've heard it a million times: it's all about the data. The same is true on the client side. XHTML strongly embraces the separation of content and presentation, and brings XML's syntactical logic, as well as extensible opportunities, to the client-side table.

XHTML 1.0, a reformulation of HTML as an XML application, has been the W3C's Web markup recommendation (www.w3.org/TR/xhtml1/) since January 26, 2000. That's more than a year now, but client-side authors and developers of popular authoring software have been slow on the take. Much of the problem lies in the fact that XHTML is misunderstood and not well publicized. Some client-side authors don't see it as having any special advantages, and many critics have claimed that XHTML simply won't be widely adopted. This may well be proven out. XHTML has been almost completely missed by the vast majority of entry- and mid-level professionals.

Ignoring or overlooking XHTML is problematic for the professional developer. Whether it's a useful client-side methodology remains a personal question. However, knowing what it is, why it is, and how it may or may not effectively aid the work you do allows you to make an informed, empowered decision about the technologies you choose to employ.

XHTML: What and Why
In simple terms, writing documents in XHTML means that instead of authoring that old familiar HTML, you are in essence writing XML. XML, in XHTML 1.0, employs HTML as its vocabulary. So elements and attributes are not arbitrary - they're drawn directly from HTML. Similarly, XML syntax rules are applied.

But how does this help client-side authors? The answer is simple. How many of you have honestly paid much attention to the HTML you generate? Some of you will certainly say you do, but most developers - like most Web designers - are guilty of a slapdash attitude toward HTML. It's not your fault. HTML has become sloppy, in part because it's been bent in many directions to accommodate the rapid growth of the Web. And browsers are extremely forgiving of poor markup. Nothing has demanded that you write clean documents because for the most part you haven't had to.

The problems resulting from this are manifold. First, there's no consistency in markup from one HTML author to the next. They've each got their own methodology - some write elements in uppercase, others in lowercase. Quotes are sometimes in use, sometimes not. Looking under the hood at even the most high-end site is usually not a pretty experience. So adding a little syntactical rigor to the mix via XHTML gets authors on the same page, if you'll pardon the pun. That can make for a much smoother workflow among teams.

XHTML 1.0 focuses heavily on getting markup cleaned up. But XHTML has another goal, too, and that's to extend to user agents beyond the Web browser: PDAs, smart phones, set-top boxes, and other alternative and wireless devices. Streamline and strengthen the markup, and you've got a stronger base from which to extend it. That's a logical and rational idea.

Another argument made in XHTML's defense - and it's a controversial one but I buy into it - is that it helps the client-side author who has XML phobia to begin moving into the XML arena via familiar means. I like this argument because as an educator, I've seen proof that it works. Take entry- or mid-level Web authors, teach them XHTML, and suddenly you can also teach them other XML applications: WML, SMIL, SVG. The light bulb goes on because they're operating in an environment that's familiar - HTML. The XML kind of sneaks in via document structure and syntactical rules.

Brass Tacks: XHTML Document Structure
To gain a better idea of how XHTML 1.0 works, let's first examine its document structure.
Ideally, an XML document begins with an XML declaration:

<?xml version="1.0" encoding="UTF-8"?>
But XHTML documents are most often viewed using popular Web browsers, which in some cases will render anything with an XML declaration as text. So for XHTML 1.0, the W3C recommends (but does not require) that the XML declaration be intact. Most Web authors leave it off.

Next comes the DTD, which is required. With XHTML 1.0, you can choose from three public DTDs: strict, transitional, or frameset. Developers working with HTML 4.0 will be familiar with these DTDs and know that the strict DTD uses the most limited set of elements and attributes of the three, basing much of its selection on the idea that presentation and structure must be separate. So you won't find the font element in a strict document. Transitional documents, however, are more flexible, understanding that Web authors must make some accommodations in order to achieve the best interoperability possible. Frameset documents are limited to framesets and can employ elements from strict or transitional DTDs.

For a strict XHTML 1.0 document, you'll use the following declaration:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/ xhtml1-strict.dtd">

If you want to write your document in accordance with the transitional DTD, you'll use:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/ xhtml1-transitional.dtd">
Finally, if you're authoring a frameset, you'll use this declaration:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/ xhtml1-frameset.dtd">
It's important to remember that there are no exceptions to the rule here. You must declare the proper DTD in your XHTML 1.0 document.

Now it's time to add the namespace to the root. In XHTML 1.0 the root element is html. The root and namespace is also a requirement, and is written as follows:

<html xmlns="http://www.w3.org/1999/xhtml">
Listing 1 shows a strict document template using the XML declaration. In Listing 2 I show a transitional document template using a meta workaround for document encoding should you choose not to use the XML declaration.

Get Tough: XHTML Syntax
Now that you've got the document structure down, it's time to explore the syntactical rules that XHTML 1.0 embodies:

  • Must be well formed
  • Is case specific
  • Insists on closing tags for nonempty elements, and termination of empty elements with a trailing slash
  • Demands that all attribute values be quoted Let's take a closer look.

Well-Formedness
Remember, Web browsers are built to forgive. That's one reason they're so bloated; they have to be able to interpret such a wide variety of markup styles. And most browsers will forgive ill-formed syntax. Try the following poorly formed bit of HTML in a browser:

<b><i>An ill-formed bit of HTML</b></i>
In common browsers such as MSIE and NN, this markup will appear in both bold and italics. However, if you examine the HTML, you'll see that the tags are improperly nested. If this markup were well formed, the tags would nest properly:
<b><i>A well-formed bit of HTML</i></b>
XHTML 1.0 must be well formed to be valid XHTML. A little trick I use to make sure I've nested my tags properly is to draw an imaginary line from the opening tag to its closing companion. If the lines don't intersect, it's properly nested and therefore well formed. Intersecting lines will indicate improperly nested, ill-formed markup.

Case Specificity
As you're already aware, XML is case sensitive:

<PRODUCT>
</PRODUCT>
and
<product>
</product>
are two different tag sets.

HTML, on the other hand, is not case specific:

<P align="right">
</P> is the same as: <p ALIGN="right">
</p>
XHTML is case specific. In every instance all elements and attribute names must be lower case:
<p align="right">
</p>
Note that attribute values can be in upper- or lowercase as necessary to accommodate file names, code strings, and URIs.

Element Handling
XHTML 1.0 adopts the XML method of closing all nonempty elements and terminating empty elements with a trailing slash. In HTML you can write the following:

<ul>
<li>list item 1
<li>list item 2
<li>list item 3
</ul>

but in XHTML, you must close the nonempty element:

<ul>
<li>list item 1</li>
<li>list item 2</li>
<li>list item 3</li>
</ul>
One of the more obvious places this occurs is with the paragraph <p> tag. You must close all nonempty elements, no exceptions.

If an element is empty (no content), it must terminate. In XML this is done by using a trailing slash as follows:

<br/>
But many Web browsers will choke on this method and subsequently not render a page or render it improperly. a workaround is to add a space before the slash. This allows all empty elements to be properly rendered. A few examples:
<img />
<hr />
<meta />
<link />
As with nonempty elements, there can be no exception to the rules. You must terminate the element accordingly.

Quoth the Attribute Value...
One of the more frustrating things about HTML - at least to my eye - is the arbitrariness of attribute value quoting. In HTML it's a now-you-see-it, now-you-don't phenomenon. So you can have:

<img src="my.jpg" border="1" width=400 height=200 alt="company logo">
or any combination of attribute value quotations you like. In most instances a browser will properly render the markup whether you've quoted the attribute value or not.

XHTML insists that you quote all attribute values, leaving nothing to chance:

<img src="my.jpg" border="1" width="400" height="200" alt="company logo" />

Not so hard, really
as you can now see, XHTML 1.0 is really no great challenge. Does it mean employing a little more care when creating documents? Yes. Does it mean watching your syntax? Absolutely. But with a few minor adjustments you can have clean markup that works in today's browsers with as close-to-perfect interoperability as HTML and still complies with W3C recommendations.

Advancing Notions: Modularization of XHTML
So what's a little cleanliness, anyway? Critics of XHTML have pointed out that changing habits just to write cleaner documents doesn't provide much incentive. It's time consuming and why on earth would you want to go back and rewrite hundreds, possibly thousands, of Web documents just to comply with a W3C recommendation when those documents function perfectly well? I can't, and won't, argue this point. It's too strong an argument. But if you're interested in moving toward extensibility, want to create consistent documents organization-wide, and want to assist your client-side authors in expanding their markup horizons, working with XHTML makes sense.

While XHTML 1.0 offers little option for extensibility - you've got three set DTDs and a specific namespace - the modularization of XHTML does offer expansion. Modularization of XHTML, which allows for the use of XML DTDs and provides the means to create subsets and extensions to XHTML, takes XHTML 1.0 from its limited place closer to its goal of working for numerous user agents. As of this writing, modularization of XHTML is a Candidate Rec-ommendation of the W3C (www.w3.org/TR/2000/CR-xhtml-modularization-20001020/).

Modularization of XHTML is a decomposition of HTML as we know it today. Instead of lumping markup methods such as managing text, images, tables, and forms, modularization breaks these things into separate modules. Then, using XML DTDs (an implementation of XML schemas is also under discussion), authors can pull together a subset of XHTML using only those modules necessary to accomplish a given task.

If you put modularization in the context of alternative device design, the rationale for XHTML begins to make a lot of sense. Many alternative devices simply don't have the processing, RAM, and video power to handle HTML's original functions. So why have all the overhead? A streamlined markup language using only those modules necessary for the device means faster, customizable delivery to equally streamlined optimized user agents.

A perfect example of modularization exists in XHTML Basic (www.w3.org/TR/xhtml-basic/), a subset of XHTML 1.1, made up of specific modules that apply to wireless devices such as PDAs, smart phones, and smart pagers. These devices are limited in their processing power, so XHTML Basic supplies those modules only for markup that make sense, such as text, links, images, very basic tables, and forms. Frames or scripting demand processing power, so they're left out of the subset. XHTML Basic, at this writing a Proposed Recommendation of the W3C, looks just like XHTML, but of course any element that falls into a module not set forth in the recommendation can't be used in a valid XHTML Basic document. However, you can extend XHTML Basic if you want to. This enables the creation of additional subsets and extensions.

Listing 3 shows a simple XHTML Basic page suitable for display on a small, wireless device such as a PDA. The listing clearly illustrates how XHTML Basic uses the structural elements set forth in XHTML 1.0, only this time the DTD that's declared is for XHTML Basic itself. The namespace is the same, as are the syntactical methodologies.

Bring It On Home
The developer who's empowered with knowledge can make better decisions. Whether you embrace client-side XML in the form of XHTML is up to you. But a careful survey of your needs and directions will help answer the question of whether XHTML will be useful in your unique situation. Being aware of what's happening with XHTML and its goals will keep you at the ready should your circumstances require you to develop not only for the Web of tomorrow, but for the wireless world and beyond.

More Stories By Molly E. Holzschlag

Molly E. Holzschlag is the executive editor of WebReview.com. She is the author of 16 books on Internet and Web design and development topics, including her most recent, Special Edition Using XHTML, from Que. You can visit her Web site at www.molly.com.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
China Unicom exhibit at the 19th International Cloud Expo, which took place at the Santa Clara Convention Center in Santa Clara, CA, in November 2016. China United Network Communications Group Co. Ltd ("China Unicom") was officially established in 2009 on the basis of the merger of former China Netcom and former China Unicom. China Unicom mainly operates a full range of telecommunications services including mobile broadband (GSM, WCDMA, LTE FDD, TD-LTE), fixed-line broadband, ICT, data communica...
SYS-CON Events announced today that CA Technologies has been named “Platinum Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CA Technologies helps customers succeed in a future where every business – from apparel to energy – is being rewritten by software. From ...
SYS-CON Events announced today that MobiDev, a client-oriented software development company, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex softw...
SYS-CON Events announced today that Cloud Academy will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Cloud Academy is the industry’s most innovative, vendor-neutral cloud technology training platform. Cloud Academy provides continuous learning solutions for individuals and enterprise teams for Amazon Web Services, Microsoft Azure, Google Cloud Platform, and the most popular cloud computing technologies. Ge...
SYS-CON Events announced today that Loom Systems will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Founded in 2015, Loom Systems delivers an advanced AI solution to predict and prevent problems in the digital business. Loom stands alone in the industry as an AI analysis platform requiring no prior math knowledge from operators, leveraging the existing staff to succeed in the digital era. With offices in S...
"My role is working with customers, helping them go through this digital transformation. I spend a lot of time talking to banks, big industries, manufacturers working through how they are integrating and transforming their IT platforms and moving them forward," explained William Morrish, General Manager Product Sales at Interoute, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
With billions of sensors deployed worldwide, the amount of machine-generated data will soon exceed what our networks can handle. But consumers and businesses will expect seamless experiences and real-time responsiveness. What does this mean for IoT devices and the infrastructure that supports them? More of the data will need to be handled at - or closer to - the devices themselves.
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm.
My team embarked on building a data lake for our sales and marketing data to better understand customer journeys. This required building a hybrid data pipeline to connect our cloud CRM with the new Hadoop Data Lake. One challenge is that IT was not in a position to provide support until we proved value and marketing did not have the experience, so we embarked on the journey ourselves within the product marketing team for our line of business within Progress. In his session at @BigDataExpo, Sum...
The taxi industry never saw Uber coming. Startups are a threat to incumbents like never before, and a major enabler for startups is that they are instantly “cloud ready.” If innovation moves at the pace of IT, then your company is in trouble. Why? Because your data center will not keep up with frenetic pace AWS, Microsoft and Google are rolling out new capabilities In his session at 20th Cloud Expo, Don Browning, VP of Cloud Architecture at Turner, will posit that disruption is inevitable for c...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 20th International Cloud Expo, which will take place on June 6–8, 2017, at the Javits Center in New York City, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
SYS-CON Events announced today that Ocean9will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Ocean9 provides cloud services for Backup, Disaster Recovery (DRaaS) and instant Innovation, and redefines enterprise infrastructure with its cloud native subscription offerings for mission critical SAP workloads.
SYS-CON Events announced today that Cloudistics, an on-premises cloud computing company, has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Cloudistics delivers a complete public cloud experience with composable on-premises infrastructures to medium and large enterprises. Its software-defined technology natively converges network, storage, compute, virtualization, and management into a ...
SYS-CON Events announced today that T-Mobile will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on ...
SYS-CON Events announced today that Addteq will exhibit at SYS-CON's DevOps Summit at Cloud Expo, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Addteq specializes in creating innovative solutions to solve business processes through the use of DevOps automation. Addteq was founded on the firm belief that automation is essential for successful software releases. Addteq's products and services are centered around the fundamental approach of understanding the pr...
Keeping pace with advancements in software delivery processes and tooling is taxing even for the most proficient organizations. Point tools, platforms, open source and the increasing adoption of private and public cloud services requires strong engineering rigor - all in the face of developer demands to use the tools of choice. As Agile has settled in as a mainstream practice, now DevOps has emerged as the next wave to improve software delivery speed and output. To make DevOps work, organization...
SYS-CON Events announced today that SoftLayer, an IBM Company, has been named “Gold Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. SoftLayer, an IBM Company, provides cloud infrastructure as a service from a growing number of data centers and network points of presence around the world. SoftLayer’s customers range from Web startups to global enterprises.
SYS-CON Events announced today that Infranics will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Since 2000, Infranics has developed SysMaster Suite, which is required for the stable and efficient management of ICT infrastructure. The ICT management solution developed and provided by Infranics continues to add intelligence to the ICT infrastructure through the IMC (Infra Management Cycle) based on mathemat...
"I think that everyone recognizes that for IoT to really realize its full potential and value that it is about creating ecosystems and marketplaces and that no single vendor is able to support what is required," explained Esmeralda Swartz, VP, Marketing Enterprise and Cloud at Ericsson, in this SYS-CON.tv interview at @ThingsExpo, held June 7-9, 2016, at the Javits Center in New York City, NY.
The buzz continues for cloud, data analytics and the Internet of Things (IoT) and their collective impact across all industries. But a new conversation is emerging - how do companies use industry disruption and technology enablers to lead in markets undergoing change, uncertainty and ambiguity? Organizations of all sizes need to evolve and transform, often under massive pressure, as industry lines blur and merge and traditional business models are assaulted and turned upside down. In this new da...