|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.
With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
Feb. 13, 2016 02:00 PM EST Reads: 251
SYS-CON Events announced today that Avere Systems, a leading provider of enterprise storage for the hybrid cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Avere delivers a more modern architectural approach to storage that doesn’t require the overprovisioning of storage capacity to achieve performance, overspending on expensive storage media for inactive data or the overbuilding of data centers ...
Feb. 13, 2016 01:30 PM EST Reads: 140
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
Feb. 13, 2016 12:45 PM EST Reads: 469
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
Feb. 13, 2016 12:00 PM EST Reads: 470
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 ad...
Feb. 13, 2016 12:00 PM EST Reads: 442
SYS-CON Events announced today that Men & Mice, the leading global provider of DNS, DHCP and IP address management overlay solutions, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. The Men & Mice Suite overlay solution is already known for its powerful application in heterogeneous operating environments, enabling enterprises to scale without fuss. Building on a solid range of diverse platform support,...
Feb. 13, 2016 11:45 AM EST Reads: 270
In most cases, it is convenient to have some human interaction with a web (micro-)service, no matter how small it is. A traditional approach would be to create an HTTP interface, where user requests will be dispatched and HTML/CSS pages must be served. This approach is indeed very traditional for a web site, but not really convenient for a web service, which is not intended to be good looking, 24x7 up and running and UX-optimized. Instead, talking to a web service in a chat-bot mode would be muc...
Feb. 13, 2016 11:45 AM EST Reads: 312
More and more companies are looking to microservices as an architectural pattern for breaking apart applications into more manageable pieces so that agile teams can deliver new features quicker and more effectively. What this pattern has done more than anything to date is spark organizational transformations, setting the foundation for future application development. In practice, however, there are a number of considerations to make that go beyond simply “build, ship, and run,” which changes ho...
Feb. 13, 2016 11:30 AM EST Reads: 280
WebSocket is effectively a persistent and fat pipe that is compatible with a standard web infrastructure; a "TCP for the Web." If you think of WebSocket in this light, there are other more hugely interesting applications of WebSocket than just simply sending data to a browser. In his session at 18th Cloud Expo, Frank Greco, Director of Technology for Kaazing Corporation, will compare other modern web connectivity methods such as HTTP/2, HTTP Streaming, Server-Sent Events and new W3C event APIs ...
Feb. 13, 2016 11:30 AM EST
SYS-CON Events announced today that AppNeta, the leader in performance insight for business-critical web applications, will exhibit and present at SYS-CON's @DevOpsSummit at Cloud Expo New York, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. AppNeta is the only application performance monitoring (APM) company to provide solutions for all applications – applications you develop internally, business-critical SaaS applications you use and the networks that deli...
Feb. 13, 2016 11:30 AM EST Reads: 445
Microservices are all the rage right now — and the industry is still learning, experimenting, and developing patterns, for successfully designing, deploying and managing Microservices in the real world. Are you considering jumping on the Microservices-wagon? Do Microservices make sense for your particular use case? What are some of the “gotchas” you should be aware of? This morning on #c9d9 we had experts from popular chat app Kik, SMB SaaS platform Yodle and hosted CI solution Semaphore sha...
Feb. 13, 2016 11:15 AM EST
Microservices are a type of software architecture where large applications are made up of small, self-contained units working together through APIs that are not dependent on a specific language. Each service has a limited scope, concentrates on a specific task and is highly independent. This setup allows IT managers and developers to build systems in a modular way. In his book, “Building Microservices,” Sam Newman said microservices are small, focused components built to do a single thing very w...
Feb. 13, 2016 07:45 AM EST Reads: 108
How is your DevOps transformation coming along? How do you measure Agility? Reliability? Efficiency? Quality? Success?! How do you optimize your processes? This morning on #c9d9 we talked about some of the metrics that matter for the different stakeholders throughout the software delivery pipeline. Our panelists shared their best practices.
Feb. 13, 2016 06:00 AM EST Reads: 129
The (re?)emergence of Microservices was especially prominent in this week’s news. What are they good for? do they make sense for your application? should you take the plunge? and what do Microservices mean for your DevOps and Continuous Delivery efforts? Continue reading for more on Microservices, containers, DevOps culture, and more top news from the past week. As always, stay tuned to all the news coming from@ElectricCloud on DevOps and Continuous Delivery throughout the week and retweet/favo...
Feb. 13, 2016 04:00 AM EST Reads: 251
The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
Feb. 13, 2016 03:45 AM EST Reads: 251
In a previous article, I demonstrated how to effectively and efficiently install the Dynatrace Application Monitoring solution using Ansible. In this post, I am going to explain how to achieve the same results using Chef with our official dynatrace cookbook available on GitHub and on the Chef Supermarket. In the following hands-on tutorial, we’ll also apply what we see as good practice on working with and extending our deployment automation blueprints to suit your needs.
Feb. 13, 2016 03:00 AM EST Reads: 101
Father business cycles and digital consumers are forcing enterprises to respond faster to customer needs and competitive demands. Successful integration of DevOps and Agile development will be key for business success in today’s digital economy. In his session at DevOps Summit, Pradeep Prabhu, Co-Founder & CEO of Cloudmunch, covered the critical practices that enterprises should consider to seamlessly integrate Agile and DevOps processes, barriers to implementing this in the enterprise, and pr...
Feb. 13, 2016 03:00 AM EST Reads: 476
If we look at slow, traditional IT and jump to the conclusion that just because we found its issues intractable before, that necessarily means we will again, then it’s time for a rethink. As a matter of fact, the world of IT has changed over the last ten years or so. We’ve been experiencing unprecedented innovation across the board – innovation in technology as well as in how people organize and accomplish tasks. Let’s take a look at three differences between today’s modern, digital context...
Feb. 13, 2016 02:45 AM EST Reads: 254
Sensors and effectors of IoT are solving problems in new ways, but small businesses have been slow to join the quantified world. They’ll need information from IoT using applications as varied as the businesses themselves. In his session at @ThingsExpo, Roger Meike, Distinguished Engineer, Director of Technology Innovation at Intuit, showed how IoT manufacturers can use open standards, public APIs and custom apps to enable the Quantified Small Business. He used a Raspberry Pi to connect sensors...
Feb. 13, 2016 02:30 AM EST Reads: 388
The principles behind DevOps are not new - for decades people have been automating system administration and decreasing the time to deploy apps and perform other management tasks. However, only recently did we see the tools and the will necessary to share the benefits and power of automation with a wider circle of people. In his session at DevOps Summit, Bernard Sanders, Chief Technology Officer at CloudBolt Software, explored the latest tools including Puppet, Chef, Docker, and CMPs needed to...
Feb. 13, 2016 02:30 AM EST Reads: 376