|By Steve Close||
|November 20, 2005 04:45 AM EST||
I believe that there is a strong tendency for developers to think of Web services as methods. In reality it is not that simple. A Web service defines an XML conversation between client and server. Yet, when a developer sits down to create Web services he or she usually starts by creating a method.
From that starting point it is easy to get a software toolkit to turn your method into a Web service. By default or with a few settings you can allow the toolkit to define the conversation around your method. This method-first development technique works, especially for small or pilot projects, but it is not the best approach. A contract-first approach results in better long-term development, interoperability, and maintenance.
Convincing a development team to work contract-first is not as simple as it might seem. You have to convince the team to spend more effort on unfamiliar languages like XML Schema and WSDL, and rely less on familiar languages such as Java or C#. With that said, there are good reasons to code your Web service the hard way - contract-first. In this article we will look at six good reasons to develop Web services contract-first instead of method-first. By the end of this article I hope you will see that contract-first is a superior way to create Web services and will save you time and money.
Before we delve into the six reasons, I want to establish the difference between method-first and contract-first Web services. We can walk through the basic steps of both styles of Web services creation using a simple service. This will allow me to show some code and remove the abstractness from the topic. Forgive me for using an example that has been repeated countless times. If you're an old pro at Web services skip ahead to the "Reason 1" heading. The following code is a Calculator with one method. My preferred weapons are Java and Apache Axis, so all examples will be coded in Java. Your choice of language or platform should have little effect on which way you will make Web services. (see Figure 1)
Step1: Create a method that will become a Web service. The code below provides simple add method that will be turned into a Web service.
public int add(op1, op2)
return op1 + op2;
Step 2: Run this method through a software toolkit that turns it into a Web service. There are many of these toolkits on the market. It might be as simple as adding an attribute, or saving the source code to a different extension. For the rest of this article we will call that machine the Web service toolkit. (see Figure 2)
Step 3: Deploy it to some Web server. The server will provide HTTP handling and leave you with a very simple Web service. Web service toolkits automatically create XML conversion code and a Web service description or WSDL (pronounced wizdle) document. This WSDL document is the key to getting a client to call your Web service and will play a prominent roll in contract-first thinking.
Step 4: A client can now obtain the WSDL document and create a client through your Web service. The cool thing is that the client can basically treat the Web service like a regular method call. Although XML is being passed via HTTP following the rules of SOAP, the client can be created very easily and the client doesn't need to know about the XML payload. (see Figure 3)
Taking a quick look at contract-first development, we can clearly see the differences between method-first and contract-first. In contract-first Web services you first create the WSDL document. The WSDL might have supporting XML Schema documents as well. As you can see from Listing 1, the WSDL code is a bit longer and more involved than the simple Java method. In fact, when you look at it in such a simple example, it almost seems ridiculous to suggest that you might write the WSDL before you write the Java code, but that is exactly what I'm suggesting. The steps to create the Web service are similar to what we've already seen, but kind of in reverse.
- Step 1: Create the WSDL and supporting Schema
- Step 2: Generate the service from the WSDL
Reason 1: Schema Is More Descriptive
Data types in Java and C# and other languages are described only in code, which is not shared with the client. Clients are generated via the WSDL document. Clients don't have the full definition of the data types unless you include that information in the XML Schema document. As a very simple example, say you are passing in a Person that consists of a firstName, middleInitial, and a lastName. In code this is simple, but some of the data may not be required. Say you want to require the firstName and lastName, but the middle initial is optional. If your WSDL is automatically generated, it is likely to turn out like Listing 2. The middleInitial is created by default, but with the XML Schema language we can get much more descriptive. With this simple example we can easily make the middleInitial optional by including one little attribute called minOccurs like the code below.
minOccurs="0" type="xs:string" />
I hope this simple example illustrates how schema can be more descriptive, but it is such a tiny example. Imagine a rich set of data, not just a simple person. If you want your clients to understand that the quantity element can only be non-negative integers, or have them understand the pattern that the SKU number must be three letters followed by a hyphen and four numbers, that can be described in XML Schema. By relying on the tool to generate the proper schema, you are passing only a vague description of the data where an e-mail address becomes a string and a month is an integer that can be negative.
Knowing that the WSDL is your client's interface it should be obvious that you want to make it as accurate and descriptive as possible. That might not be enough to write the WSDL first. You could still modify the WSDL after the fact and pass that out to your clients, but we have more reasons to go.
Reason 2: Your Language Is Not Alone
To understand the "we are not alone" idea, we only need to expand the Web service example a bit. You create a Web service and you require that data representing a customer be sent to invoke the service. You may have put some time into the customer type and you realize it should be shared. Other departments also use the same entity in their services, but wait, here's the problem. You code in C#, they code in Java. You can't just centralize the code. They need to convert it to Java. No big deal, as easily done as said practically, but what if the definition of a customer changes? If the Java coders change the customer your two versions no longer match. Which version is the "central" or "master" customer type? Do I need to change the Java code every time I change the C#? How do you communicate the change to the other team?
|Jeff Kessler 12/13/05 05:32:16 PM EST|
What would be a good followup to this article would be a short tutorial on WSDL first development.
|Agree 11/20/05 04:52:20 AM EST|
>> Contract-first makes following standards easier
|Christian Weyer 11/07/05 12:34:29 PM EST|
There is free tool support for building your WSDL without having to know all those insane details:
Even for Java Eclipse:
For an in-depth coverage of contract-first design and development with .NET see this article here:
|Patrick Rooney 10/26/05 05:38:04 PM EDT|
Excellent article Steve! The approach of focusing on the data to ensure consistency and re-use of services across the enterprise is very important, and not well understood by many developers. In our implementation of SOA across IBM we are using a similar approach. We have defined our own "Enterprise Integration Messaging Specification", which is based on the OAGIS (8.0) XML Schema messaging standard, to establish re-usable message payload structural and data dictionary schema types that can be re-used across the enterprise. These are used to define the parameters (data schema types) that are sent in the messages (Service Operation parameters). The wsdl is created and from these the Services are created.
The 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding bu...
Jul. 4, 2015 09:30 AM EDT Reads: 821
The last decade was about virtual machines, but the next one is about containers. Containers enable a service to run on any host at any time. Traditional tools are starting to show cracks because they were not designed for this level of application portability. Now is the time to look at new ways to deploy and manage applications at scale. In his session at 16th Cloud Expo, Jake Moshenko, Product Manager at CoreOS, examined how CoreOS + Quay.io fit into the development lifecycle from pushing gi...
Jul. 4, 2015 09:30 AM EDT Reads: 2,357
The 5th International DevOps Summit, co-located with 17th International Cloud Expo – being held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the ...
Jul. 4, 2015 09:15 AM EDT Reads: 789
Sharding has become a popular means of achieving scalability in application architectures in which read/write data separation is not only possible, but desirable to achieve new heights of concurrency. The premise is that by splitting up read and write duties, it is possible to get better overall performance at the cost of a slight delay in consistency. That is, it takes a bit of time to replicate changes initiated by a "write" to the read-only master database. It's eventually consistent, and it'...
Jul. 4, 2015 09:00 AM EDT Reads: 1,850
DevOps Summit, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development...
Jul. 4, 2015 08:45 AM EDT Reads: 915
"Plutora provides release and testing environment capabilities to the enterprise," explained Dalibor Siroky, Director and Co-founder of Plutora, in this SYS-CON.tv interview at @DevOpsSummit, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 4, 2015 08:00 AM EDT Reads: 1,317
Overgrown applications have given way to modular applications, driven by the need to break larger problems into smaller problems. Similarly large monolithic development processes have been forced to be broken into smaller agile development cycles. Looking at trends in software development, microservices architectures meet the same demands. Additional benefits of microservices architectures are compartmentalization and a limited impact of service failure versus a complete software malfunction. ...
Jul. 4, 2015 07:30 AM EDT Reads: 1,208
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at @ThingsExpo, James Kirkland, Red Hat's Chief Arch...
Jul. 4, 2015 07:00 AM EDT Reads: 1,024
17th Cloud Expo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterprises ar...
Jul. 4, 2015 06:00 AM EDT Reads: 842
This week we're attending SYS-CON Event's DevOps Summit in New York City. It's a great conference and energy behind DevOps is enormous. Thousands of attendees from every company you can imagine are focused on automation, the challenges of DevOps, and how to bring greater agility to software delivery. But, even with the energy behind DevOps there's something missing from the movement. For all the talk of deployment automation, continuous integration, and cloud infrastructure I'm still not se...
Jul. 3, 2015 07:00 PM EDT Reads: 2,243
IT data is typically silo'd by the various tools in place. Unifying all the log, metric and event data in one analytics platform stops finger pointing and provides the end-to-end correlation. Logs, metrics and custom event data can be joined to tell the holistic story of your software and operations. For example, users can correlate code deploys to system performance to application error codes. In his session at DevOps Summit, Michael Demmer, VP of Engineering at Jut, will discuss how this can...
Jul. 3, 2015 07:00 PM EDT Reads: 961
The most often asked question post-DevOps introduction is: “How do I get started?” There’s plenty of information on why DevOps is valid and important, but many managers still struggle with simple basics for how to initiate a DevOps program in their business. They struggle with issues related to current organizational inertia, the lack of experience on Continuous Integration/Delivery, understanding where DevOps will affect revenue and budget, etc. In their session at DevOps Summit, JP Morgenthal...
Jul. 3, 2015 02:45 PM EDT Reads: 948
Data center models are changing. A variety of technical trends and business demands are forcing that change, most of them centered on the explosive growth of applications. That means, in turn, that the requirements for application delivery are changing. Certainly application delivery needs to be agile, not waterfall. It needs to deliver services in hours, not weeks or months. It needs to be more cost efficient. And more than anything else, it needs to be really, dc infra axisreally, super focus...
Jul. 3, 2015 01:45 PM EDT Reads: 2,130
Discussions about cloud computing are evolving into discussions about enterprise IT in general. As enterprises increasingly migrate toward their own unique clouds, new issues such as the use of containers and microservices emerge to keep things interesting. In this Power Panel at 16th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the state of cloud computing today, and what enterprise IT professionals need to know about how the latest topics and trends affect t...
Jul. 3, 2015 12:30 PM EDT Reads: 1,422
Containers have changed the mind of IT in DevOps. They enable developers to work with dev, test, stage and production environments identically. Containers provide the right abstraction for microservices and many cloud platforms have integrated them into deployment pipelines. DevOps and Containers together help companies to achieve their business goals faster and more effectively. In his session at DevOps Summit, Ruslan Synytsky, CEO and Co-founder of Jelastic, reviewed the current landscape of...
Jul. 3, 2015 11:15 AM EDT Reads: 2,407
Manufacturing has widely adopted standardized and automated processes to create designs, build them, and maintain them through their life cycle. However, many modern manufacturing systems go beyond mechanized workflows to introduce empowered workers, flexible collaboration, and rapid iteration. Such behaviors also characterize open source software development and are at the heart of DevOps culture, processes, and tooling.
Jul. 2, 2015 02:15 PM EDT Reads: 1,024
SYS-CON Events announced today that JFrog, maker of Artifactory, the popular Binary Repository Manager, will exhibit at SYS-CON's @DevOpsSummit Silicon Valley, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Based in California, Israel and France, founded by longtime field-experts, JFrog, creator of Artifactory and Bintray, has provided the market with the first Binary Repository solution and a software distribution social platform.
Jul. 2, 2015 01:00 PM EDT Reads: 1,342
Conferences agendas. Event navigation. Specific tasks, like buying a house or getting a car loan. If you've installed an app for any of these things you've installed what's known as a "disposable mobile app" or DMA. Apps designed for a single use-case and with the expectation they'll be "thrown away" like brochures. Deleted until needed again. These apps are necessarily small, agile and highly volatile. Sometimes existing only for a short time - say to support an event like an election, the Wor...
Jul. 2, 2015 11:00 AM EDT Reads: 1,804
The cloud has transformed how we think about software quality. Instead of preventing failures, we must focus on automatic recovery from failure. In other words, resilience trumps traditional quality measures. Continuous delivery models further squeeze traditional notions of quality. Remember the venerable project management Iron Triangle? Among time, scope, and cost, you can only fix two or quality will suffer. Only in today's DevOps world, continuous testing, integration, and deployment upend...
Jul. 2, 2015 11:00 AM EDT Reads: 2,225
DevOps tends to focus on the relationship between Dev and Ops, putting an emphasis on the ops and application infrastructure. But that’s changing with microservices architectures. In her session at DevOps Summit, Lori MacVittie, Evangelist for F5 Networks, will focus on how microservices are changing the underlying architectures needed to scale, secure and deliver applications based on highly distributed (micro) services and why that means an expansion into “the network” for DevOps.
Jul. 2, 2015 07:45 AM EDT Reads: 2,696