Wiley 978-0-7645-4942-7 Datasheet

Brand: Wiley

Model: 978-0-7645-4942-7

Category: Software manuals

Type: Datasheet

Curl Content

Language

Fundamentals

✦✦✦✦

In This Part

Chapter 1

Introducing Curl

Chapter 2

How Curl Works

Chapter 3

Building Your First

Curl Applet with the

Surge

Lab IDE

Chapter 4

Working with Text

Chapter 5

Building Tables

Chapter 6

Adding Images,

Backgrounds, and

Borders

Chapter 7

Working with

Variables

Chapter 8

Controlling Program

Flow

Chapter 9

Creating and Using

Procedures

Chapter 10

Creating Classes

Chapter 11

Inheritance

Chapter 12

Strings and Arrays

Chapter 13

Handling Exceptions

in Curl

✦✦✦✦

PART

b4942-1 Part01.F 4/29/02 9:01 AM Page 1

b4942-1 Part01.F 4/29/02 9:01 AM Page 2

Introducing Curl

he 13 chapters in Part I provide basic information about

Curl, its architecture, and its fundamental programming

constructs. This chapter explains what Curl is, what businesses

would benefit from using it, and how to phase it into your

development process. Successive chapters discuss Curl’s

architecture, the development tools, plus the usage of text,

images, variables, control structures, procedures, and classes.

Part II, Chapters 14–18, discusses how to build a user interface

with Curl. Part III, Chapters 19–22, discusses Curl’s graphics

and multimedia capabilities. Part IV, Chapters 23–25, discusses

files and server communication. Part V, Chapters 26–28,

discusses deploying applications. Part VI, Chapters 29–30,

discusses XML and Web services.

What Is Curl Technology?

Curl Corporation provides the Surge plug-in and the Surge

Lab IDE, for viewing and creating content written in the Curl

Content Language. Users need the Surge plug-in to view Curl

content in their browser. Authors will also need the Surge Lab

IDE to create Curl content.

The terms Curl Surge plug-in, Surge plug-in, and plug-in are

used interchangeably, as are the terms Curl Content language,

and just Curl. Curl, Surge, and Surge Lab are trademarks of

Curl Corporation.

This chapter is an overview of each component. Successive

chapters cover each component in detail.

Curl content language

Curl combines the worlds of document markup, scripting, and

object-oriented programming into a single language. Curl

sprung from MIT’s famed Laboratory for Computer Science

and later was spun off into Curl Corporation (

www.curl.com).

CHAPTER

✦✦✦✦

In This Chapter

Understanding Curl

technology

Learning when to use

Curl

Integrating Curl into

your development

process

✦✦✦✦

c4942-1 ch01.F 4/29/02 9:01 AM Page 3

Part I ✦ Curl Content Language Fundamentals

Curl was specifically designed to have a “gentle slope” learning curve. This means

that no matter what your current knowledge of Curl, learning the next level of func-

tionality is only slightly harder.

At one end of the learning curve, Curl is a simple markup language that you can use

in place of HTML. Authors can learn this aspect of Curl in a few minutes. Sliding up

the curve a notch, you can create simple interface elements such as buttons and

drop-down menus, with variables and local data validation. At the higher end of the

learning curve, you can have object-oriented client/server applications with 3D

graphics and other advanced tools.

Borrowing from Dylan, an object-oriented language, Curl combines the flexibility of

dynamic languages (Smalltalk, Scheme) with the speed of static-typed languages

(C++, Eiffel). This combination also provides a gentle slope for development styles.

When prototyping, Curl’s support of typeless variables and class variables provides

flexibility and speed of development. For commercial code, you can add more static

typing to improve correctness and execution speed.

Surge Lab IDE

The Surge Lab provides all the tools an author or developer needs to create Curl

content. In theory, Curl content could be written in any text editor, but the Surge

Lab provides much more functionality and it’s free.

The Surge Lab includes its own syntax-aware Source Editor, API Viewer, Debugger,

Object Inspector, and Release Tool for packaging Curl code. The Lab also allows

you to run applets locally without needing a Web server. See Chapter 3 for a tutorial

on the Surge Lab.

Surge plug-in

The Surge plug-in provides a sophisticated runtime environment for running Curl

code securely. The plug-in includes a just-in-time (JIT) compiler and a unique

security model that protects the user’s computer from the issues that have

plagued mobile code in the past. Developers can affect the executable code by

sending directives to the JIT compiler. These directives can control the trade-offs

between the freedom of typeless programming versus code-safety and speed.

The Surge plug-in also permits a single user to compile and run multiple versions

of Curl. If the applet needs a newer version of Curl, the plug-in gives the user the

option of downloading the newer module. This solves the thorny problem of

backward compatibility that haunts many other plug-ins.

Finally, the plug-in acts as the traffic cop that enforces many of Curl’s security

features. These include

✦ Verifying an applet’s right to

include or import Curl files from the host and

comparing package versions to ensure compatibility

c4942-1 ch01.F 4/29/02 9:01 AM Page 4

Chapter 1 ✦ Introducing Curl

✦ Preventing unprivileged applets from accessing local files

✦ Protecting intellectual property by prohibiting users from viewing the Curl

source code

See Chapter 2 for more details on Curl’s security features.

Surge Control Panel

The Surge Control Panel allows the user to control runtime options for security,

debugging, and general preferences. This feature is most frequently used to allow

applets from a particular host or directory to run with privileged access.

Console window

The Console window shows system warning and error messages. Also, any mes-

sages using the

output command (normally, only used while debugging) appear in

the Console window.

Platform Independence

Curl has been explicitly designed as a cross-platform language, suitable for reaching

a wide audience across the Web. Surge only accepts Curl source code, either raw

or compressed and preprocessed in .pcurl files, and compiles each applet on the

target machine before running it. This local compilation, rather than reliance on

externally produced executables or intermediate byte-codes, permits true platform

independence.

By compiling Curl on the client machine, Surge always knows the exact run-time

environment the applet will face when executing. This allows Surge to take advan-

tage of local machine resources, such as hardware graphics rendering, when

possible, but does not depend on them. This late-binding aspect of the Curl/Surge

architecture yields better platform independence and produces faster executables.

Curl Corporation’s business approach to platform independence is equally crucial.

They are creating the Surge run time for each platform themselves. This allows Curl

Corporation to ensure that Surge works uniformly across all platforms and to avoid

the Java debacle of “write once, debug everywhere.”

Surge currently works on the vast majority of client machines, which is to say

machines that run Microsoft Windows. Curl Corporation plans to make Surge

available on Linux and Macintosh computers; eventually, it will be on PDAs and

cell phones. Visit

www.curl.com for updates on platform availability.

Interoperability

You don’t have to throw out your current Web site to use Curl. Curl content can be

used alongside, or in place of, HTML. Curl can interoperate with other tools such as

ASP, CGI scripts, and other development tools.

c4942-1 ch01.F 4/29/02 9:01 AM Page 5

Part I ✦ Curl Content Language Fundamentals

Curl comes with the SAX (Simple API for XML) parser for XML documents. This

means that Curl speaks XML as a native language, which makes Curl applets excel-

lent front ends for XML data. This makes Curl an ideal user interface for the growing

body of SOAP/Web services. See Chapter 29 for details on using SAX with Curl.

See the CurlExamples site (

www.curlexamples.com) for specific examples of work-

ing with other tools. Also, see the “Fitting into Your Infrastructure” section, later in

this chapter, for tips on applying Curl to your current situation.

Types of Curl Technology Solutions

From a technical point of view, nearly any client-side application can be improved by

using Curl. However, there are some significant usability and business considerations.

Usability

Curl’s interactive features and local response times generally make applications sig-

nificantly easier and faster to use. This improved usability can give your application

an edge against the competition. It may even permit you to charge premium pricing

(until your competitor adopts Curl). Improved usability is one of the key reasons

companies use Curl.

As with any plug-in, however, there are the issues of startup time and installation

that must be considered. In the 1.0 release, it can take 20 or more seconds, depend-

ing on your computer, to launch the Surge plug-in the first time (of course, you can

always configure the plug-in to launch on computer startup). Furthermore, each

user needs to have downloaded and installed the Surge plug-in, which takes a few

minutes, depending on your connection speed.

As Curl/Surge becomes more ubiquitous and Surge launch times decrease (the 2.0

version of the plug-in, due out in the summer of 2002, is supposed to launch 5 times

faster than the current version), these will not be issues. For now, the Surge launch

time needs to be considered as part of the application’s usability. Public sites that

expect traffic from a wide range of users would probably not want to put Curl

content on their home page, for example.

Business models

Before discussing when to use Curl, it is useful to segment the types of application

in use today. There are two basic kinds of revenue-producing methods on the Web:

transactions fees (eBay, Amazon, Dell) and subscription fees (Wall Street Journal,

Communispace).

c4942-1 ch01.F 4/29/02 9:01 AM Page 6

Chapter 1 ✦ Introducing Curl

Things are never so neatly defined in practice, of course. A “free” site is essentially

a subscription site with a fee of zero or with a marketing area designed to sell sub-

scriptions or transactions; and an advertising site is essentially a transaction-fee

site, except that the transactions that yield money are advertising impressions to

the user.

Sites can be further categorized by whether they allow public access or private

access. These two dimensions segment Web applications into four quadrants

shown in Table 1-1. The sections below discuss how each relates to Curl.

Table 1-1

Business Models

Transaction Revenue Subscription Revenue

Public Users Amazon, eBay, Dell, etc. Wall Street Journal, Yahoo!*, etc.

Private Users Fidelity, E*Trade, etc. Communispace, Paychex, Intranets*, etc.

*Note that “free” sites, such as Yahoo!, or a corporate intranet, can be thought of as subscription sites with a fee

of zero. Free corporate sites are marketing areas designed to sell subscriptions or transactions (offline or online).

Public transaction sites

Public transaction sites include such Web poster children as Amazon, eBay, and

Dell. These sites are open to any Web user and make money when a user completes

a transaction. From a technical and operational viewpoint, this category stands to

gain the most from a Curl solution. Curl could save these high-traffic sites tremen-

dous amounts of money in reduced server and bandwidth costs.

Unfortunately, downloading the Surge plug-in presents the biggest challenge to

public transaction sites. With so many new users each day, they simply can’t insure

that the majority of users will have Surge installed on their computers.

Short term, these sites may want to start a small Curl project and create a mem-

bers-only segment of their site with a premium interface. Repeat users would be

enticed to download Surge to gain access to more sophisticated features. In effect,

this converts a segment of these sites to private transaction sites for frequent

users. Every user they entice to use the Curl application saves them money. Equally

important, as Surge becomes more prevalent, they will already have a Curl applica-

tion waiting. They can maintain their market leadership while making a smooth

transition.

Public subscription sites

Public subscription sites include paid sites, such as the Wall Street Journal online,

and sites such as Yahoo! (Think of it as a free subscription.) Again, technically and

operationally these sites would benefit tremendously from Curl.

c4942-1 ch01.F 4/29/02 9:01 AM Page 7

Part I ✦ Curl Content Language Fundamentals

For usability, the more the subscription costs, the more likely the user will be inter-

ested in Curl. When the information is free and often available in multiple places,

the user’s primary concern is usually saving time. Launching Surge slows them

down. When the information is expensive, the user is more likely to be concerned

about finding the best information. This is where the improved response time and

usability of a Curl application is worth the time it takes to launch Surge.

Free sites will probably have to wait until Surge is more readily available or until

they can create a members-only area as discussed previously.

Private transaction sites

Private transaction sites include financial sites such as Fidelity, E*Trade, and home

banking. Although these companies have a public component to their Web site, this

category refers to the features provided for registered users. Here, users can exam-

ine their account, request information, and move money around or make other

transactions. This is an excellent setting for Curl. Aside from the usual technical

and operational benefits, most users are repeat users and would be happy to have a

richer interface.

Private subscription sites

Private subscription sites include application service providers (ASPs) such as

Communispace and Paychex. In these settings, users pay a flat fee to rent the ASP’s

online application. Because users have already paid for the service, they are highly

motivated to get the best use from the site. Installing Surge is easier since the users

are known in advance.

Since ASP providers have a fixed revenue stream each month, any reduction in cost

is pure profit for them. This gives ASPs a strong incentive to use Curl.

Corporate intranets fit into this category as well. Again, think of them as a subscrip-

tion site that charges the flat fee of zero each month. This is further incentive to

keep the cost down and the user productivity high because any wasted user time is

wasting your own company’s money.

Private subscription sites are the ideal business and technical situation to use Curl.

Summary of Web business uses

Web businesses fall into four main categories. Technically and operationally, all four

categories could benefit from using Curl today. The viability of using Curl for your

business depends on how prevalent Surge is among your users.

Sites with private users (ASP services, intranets, financial services, and so on) are

perfect for using Curl today. Public subscription sites, particularly those that

charge premium prices, are also good Curl candidates. Public transaction sites,

such as Amazon, would be better using Curl in a members-only capacity until Surge

c4942-1 ch01.F 4/29/02 9:01 AM Page 8

Chapter 1 ✦ Introducing Curl

is more ingrained with the public. Once converted to Curl, however, public transac-

tion sites may have the biggest cost saving.

Fitting into Your Infrastructure

Adding any new tool to your arsenal requires both business and technical planning.

As this is a technical book, most of the chapters focus on technical learning and

planning. However, we start by discussing business planning here since it often sets

the parameters and goals for technical planning.

Business planning

The gentle slope aspect of learning Curl makes it relatively easy to add it into your

current development environment. Naturally, you will want to weigh the costs and

benefits of using Curl. Many of the benefits of Curl were already covered in this

book’s introduction, but a quick summary would be that Curl allows your applica-

tions to

✦ Provide a richer interface.

✦ Provide faster response time for your users in many cases.

✦ Provide better security for your applications.

The idea of a richer interface merits a brief elaboration. Curl permits direct manipu-

lation of the interface by your users, enabling them, for example, to resize tables,

sort data, use configurators, and rotate graphics. This creates stickier application

sessions.

On the cost side, Curl has many advantages. In the heady dot-com boom days of

the late 1990s, revenue was king and nobody cared about the cost, let alone profits.

Those days are gone, gone, gone. Back in the real world, cost is a crucial aspect of

any business’s profitability. When examining the cost of switching to a new technol-

ogy, you would normally consider

✦ Cost of hiring and training Curl developers

✦ Cost of supporting dual development environments during transition

✦ Cost of Curl development tools

✦ Cost in time and dollars to develop and code projects in Curl

✦ Cost in time and dollars to test Curl applications

✦ Cost of deploying and operating a Curl application

✦ Cost of maintenance to fix problems and extend a Curl application

c4942-1 ch01.F 4/29/02 9:01 AM Page 9

Part I ✦ Curl Content Language Fundamentals

The following sections examine each of these costs in more detail.

Hiring and training

The big win with Curl is that your development staff can focus on becoming expert

in one client-side language rather than average in many languages. The cost of

teaching developers Curl might be offset by not having to train each person in

multiple languages.

Curl is relatively easy to learn, so you won’t need to hire Curl-only developers.

Anyone can quickly learn Curl’s text formatting features; HTML experience is not

required. To use the programmatic aspects of Curl, experience with any object-

oriented language (Java, C++, Eiffel, Smalltalk, Dylan) would suffice.

Curl’s gentle slope learning curve means that whatever a person’s current experi-

ence with Curl, learning the next feature is only slightly harder. This is a remarkable

accomplishment as compared to other languages, such as C++, that require huge

time investments before one can become proficient.

In addition to books like this, developers can learn Curl from the resources listed in

“Finding Curl Information,” later in this chapter. Curl Corporation also offers hands-

on training.

Dual environment costs

Often, switching to new tools comes with the hidden cost of maintaining your

existing system while developing the new one. This means that, during the transi-

tion, you need to have staff expertise with many tools. You may even need to have

separate hosting environments. Since Curl can usually be phased into your existing

architecture, there is rarely a need to support dual development environments. (An

exception might be public transaction sites.) Thus, this cost is often zero, or very

low. “Technical planning,” later in this chapter, explains why this is true.

Development costs

Using Curl, development times are similar to— or faster than — normal, once you

have trained developers. Partly, this is because Curl is a powerful language and

partly this is because your developers spend less time working around the quirks

of using multiple languages. Figure 1-1 shows how fast complexity grows when

there are more tools involved.

The graph in Figure 1-1 shows that accounting for the interactions between two

tools is 10 times easier than having five tools and 21 times easier than having seven

tools. For enhancements and bug fixes, having a uniform language makes it easier

for one developer to modify another developer’s code. Plus, Curl development tools

are free.

c4942-1 ch01.F 4/29/02 9:01 AM Page 10

Chapter 1 ✦ Introducing Curl

Figure 1-1: How more tools increase development complexity

Another benefit is that Curl-based architectures are an extension of the well-studied

client/server architectures that have been around for many years. This means that

you are not on the bleeding edge of system architecture. Instead, you can benefit

from years of industry experience in this area, further reducing risk on your project.

Testing costs

Testing current Web applications is a combinatorial mess. Figure 1-1 applies to

testers as well as to developers. If testers tried to verify a complex application for

every combination of operating system manufacturer and version, browser manu-

facturer and version, JVM version, JavaScript version, and so on, they would never

finish. This is not slighting testers, but recognition that testing is an economic

choice; testing each combination produces diminishing returns. How much are you

willing to spend to be sure? How long is the market willing to wait for your product?

What is the cost if you are wrong?

With Curl applications, the major browser combinations were already tested by

Curl Corporation when it tested Surge. Also, many Curl customers have gone before

you. Yes, it’s a nightmare, but it’s their nightmare. Since Curl version heralds ensure

your applet uses the correct version of Surge, all you need to do is test that your

application works with a specific version of Surge. You can spend more time testing

your application’s features and less on platform combinations.

Operational costs

It is generally cheaper to run Curl applications than applications based on other

Web technologies. However, your saving will depend on how many of the following

bullets apply to your site. Does your Web site:

Number of Interactions

Number of Tools

12345678910

c4942-1 ch01.F 4/29/02 9:01 AM Page 11

Part I ✦ Curl Content Language Fundamentals

✦ Deliver large pages that may include rich content?

✦ Do data-validation on the server?

✦ Dynamically create pages from templates on the server?

✦ Deliver pages that interact locally with the user (e.g., JavaScript)?

✦ Provide multiple views of the same data?

✦ Require large amounts of bandwidth to satisfy user demand?

✦ Require multiple servers to handle user load?

✦ Make money via subscription or transaction fees?

The more yes answers you had to these questions, the more money Curl is likely to

save you. Typically, for complex applications, Curl drastically reduces the amount

of data being served from your hosts and uses less CPU time. This translates

directly into lower monthly hosting and bandwidth costs.

If you answered no to all of those questions, you probably have a simple online

brochure or business card site with mostly static content. If so, then Curl may not

be the best choice for your site. If your site is already small enough that you are

using a single host with standard bandwidth, you will not save money on hosting or

bandwidth. Then again, it’s possible you might be small enough to not trigger Curl

Corporation’s billing threshold at all, in which case Curl would be free.

Technical planning

This section focuses on how best to phase Curl into your existing architecture. It is

tempting to start with the minimal disruption to your development process and

simply start by recoding your HTML pages into Curl. While this has simplicity on

its side, it might not benefit you much, which could incorrectly give a negative first

impression of Curl.

Because, in the initial version of Curl, it can take a number of seconds to launch

Surge, you want to make sure your users get a tangible benefit whenever they

launch it. It generally would not make sense, for example, to have a Curl home page

unless you expected your visitors to use your Curl-based features.

Where does it hurt?

To decide where to start, you should first identify the areas where Curl could provide

the greatest benefits. Benefits come in many flavors: faster response times, richer

features, cost savings, and so on. Naturally, you will have to decide which goal(s) to

pursue, but as a guide you should gather the following information about your site:

✦ Which pages do users view the most?

✦ Which pages are the largest to download?

✦ Which features require the most CPU time on your servers?

c4942-1 ch01.F 4/29/02 9:01 AM Page 12

Chapter 1 ✦ Introducing Curl

✦ Which features require the most disk accesses on your servers?

✦ Which features are currently most awkward for your users?

✦ Which pages have the most local user interaction?

✦ Which use cases require the most round-trips to the server?

The answers create a “pain list” of what “hurts” most about each aspect of your

site. Often, users are more elated by an improvement in a current feature than by

the addition of a new one. (Note that Marketing usually feels the opposite way.)

Users already expect new features to be perfect, so if you deliver a great new fea-

ture, they will be only modestly impressed. Users are more apt to be impressed

when you fix a daily frustration. Existing features also have the advantage of being

well understood, so you are less likely to stall on endless brainstorming aiming at

perfection. Pages or features that appear on multiple pain lists should be strongly

considered for your first foray into Curl.

Analyzing the pain

Now that you’ve identified the painful aspect of your site, you need to decide if Curl

can help. If you have high-bandwidth pages, can Curl reduce them by using client-

stored templates that only get loaded once? Where your server is using CPU time,

could Curl use the client’s CPU? If your server accesses its disk to store user-state

data, could Curl store the state information on the client? If you have multiple

servers, what would it take to eliminate one of them? Most systems have a specific

bottleneck that causes problems. Curl should be used to address one of the bottle-

necks, if possible.

Solve an easy one

This does not mean that you should find the hardest problem you can find and

tackle it first. The road of technology adoption is littered with roadkill from teams

that overpromised and fell short. If your first attempt at Curl is a failure, you may

not get a second chance.

Instead, you should take the pain list and estimate how easy or hard it would be to

solve the problem using Curl. Choose something that you think is easy or medium-

hard for your first project. If everything on your pain list is hard to solve in Curl,

pick a less critical feature even if it’s not on the list. Choosing a hard project for

your first usage of any new tool is begging for trouble. The first project is always

harder than it appears.

Consider the longer term

Since Curl can incrementally replace parts of your site, update the pain list periodi-

cally to help pick future priorities. Keep in mind that the notion of solving a current

problem was only intended to cover your first use of Curl. After you are comfort-

able with Curl, new features or enhancements should be considered as well.

c4942-1 ch01.F 4/29/02 9:01 AM Page 13

Part I ✦ Curl Content Language Fundamentals

Finding Curl Information

As Curl has expanded into daily use around the world, various resources have

emerged to help you understand Curl further. Below is a list of resources that can

help you expand your knowledge of Curl.

Curl Corporation

First and foremost, you can get definitive information at the Curl Corporation Web

sites. It you want it straight from the horse’s mouth, here is where to go.

General information

See www.curl.com for general information about Curl Corporation. This includes

product information, press releases, Curl demos, and other general information

about Curl Corporation.

Developer information

See www.curl.com/html/developers/developers.jspto connect directly to the

Curl Developer section of the site. The Curl Developer area contains FAQs, tutorials,

documentation, and discussion forums. The discussion forums are particularly

helpful now that Internet newsgroups have devolved into spam. It is not unusual to

get a response directly from Curl’s internal development team.

curlBreaker.com

curlBreaker.com is an independent organization that is committed to being “the

place to go for Curl Content Language news, tips, etc.” They offer several different

resources for Curl developers.

Web magazine

The curlBreaker.com Web magazine is an independent ‘zine for Curl developers.

The magazine covers news from the Curl world with feature articles on various Curl

topics. This is a great place to go to get independent news and analysis on Curl-

Wiley 978-0-7645-4942-7 Datasheet

Brand: Wiley

Model: 978-0-7645-4942-7

Category: Software manuals

Type: Datasheet

Download PDF

report

Wiley 978-0-7645-4942-7 Datasheet

Wiley 978-0-7645-4942-7 Datasheet

Related papers

Other documents