Welcome!

SOA & WOA Authors: Lori MacVittie, Trevor Parsons, Carmen Gonzalez, Jason Bloomberg, Keith Cawley

Related Topics: Java

Java: Article

Java Feature — What Is SCA?

A simple model for creating service-oriented applications

Service Component Architecture (SCA) is a simple model for creating service-oriented applications. This article highlights the benefits of SCA and introduces SCA concepts by walking through an example. The example has been developed using the Apache Tuscany open source project (http://incubator.apache.org/tuscany/). All the sample code in this article is licensed under the Apache License 2.0 (www.apache.org/licenses/LICENSE-2.0) and the resources with the article gives a link to the sample files. Both the Apache Tuscany and PHP SCA_SDO (http://pecl.php.net/package/sca_sdo) projects provide a free service oriented infrastructure for creating, packaging, deploying, and managing applications built with the SCA programming model.

The SCA programming model itself is described by a set of specifications that are being developed by many vendors and individuals contributing to the Open Service Oriented Architecture collaboration (www.osoa.org).

SCA
Service Oriented Architecture (SOA) is an architectural approach driven by the need to overcome the challenges of tightly coupled and department-specific applications. SOA promises benefits such as improved business agility, improved flexibility, cost reduction, and the easy sharing of information in heterogeneous and distributed environments.

SOA provides a blueprint but implementing an SOA remains a challenge. The choice of technology available to the implementer is bewildering and skills in a variety of technologies are required to be successful. Service Component Architecture (SCA) addresses the complexity of developing an SOA solution through its simple model for creating service-oriented applications for the whole enterprise - from the client to the back-end. Businesses using SCA can benefit from the following:

  • Rapid development and increase in productivity: SCA views an application as a set of connected components. It provides a simple language-neutral component model for implementing new components or reusing existing components. A component can be implemented in any language supported by an SCA runtime. SCA promotes true loose coupling by separating component implementation from the details of component composition. This bottom-up development style allows the developer to focus on developing business-related code with-out worrying about how this will fit into the overall solution.
  • Higher organizational agility and flexibility: SCA also supports a top-down development approach of creating business solutions with its flexible service assembly model. SCA components can be wired together in a composition. A component can be replaced with another component in the composition as long as they share the same contract. The composition can be adjusted to IT infrastructure requirements such as service connections, transport protocols, transactions, security, and reliable messaging. Selectable transport bindings make solutions available in the widest possible set of deployment situations.
  • Return on Investment through reuse: The SCA component model makes it very easy to leverage investments made in existing applications and services. Its standardized approach to encapsulation and interface abstraction enables service reuse through wiring and rewiring to construct new applications. SCA itself is technology-neutral and isn't intended to replace existing technology. It simply provides a component composition model that describes how new and existing services are assembled.
Figure 1 is taken from the SCA Assembly Model specification (www.osoa.org/display/Main/Service+Component+Architecture+Specifications) and shows the main artifacts of SCA.

The dark blue boxes (Component A and Component B) show components. Components are at the heart of SCA as they encapsulate business logic. Depending on runtime support, components implemented using any programming technique can be included. For example, Apache Tuscany currently supports the Java language, JavaScript, Ruby, Python, and C++ component types and provides an extension API for building new extensions.

SCA components can have properties (the yellow boxes shown at the top of components A and B). Properties control the behavior of the component and can be changed at deployment time. For example, a stock quote application might have a property that indicates the currency that stock values will be quoted in.

SCA components describe the interfaces that they expose for other components to call, shown as the green arrows on the left-hand side of the component boxes and called "services" in SCA. Components also describe the interfaces of other components that they expect to call as the business logic executes, shown as the pink arrows on the right-hand side of the component boxes and called "references" in SCA. These exposed services and references can be "wired" together to describe a working system.

The diagram shows two components, A and B, assembled together within the bounds of a larger "composite," called composite A. The SCA composite describes a collection of wired components and, as you can see, the composite also echoes those services and references that must be exposed beyond the bounds of the composite. Wiring together components within a composite is akin to building a tightly coupled application that may run in a single process. Wiring together the services and references exposed by a composite represents a more loosely coupled system where each composite may run in a separate process or processor and is connected over a network with various protocol/transport bindings. This way SCA provides a consistent model for describing standalone and distributed applications.

An Example Scenario
We'll use the fictional MostMortgage company's mortgage loan approval application to introduce SCA in more detail. The loan approval application accepts a mortgage request including the customer's details and the requested loan amount. It first checks the customer's credit to make sure the credit score meets the minimum requirement. The interest rate is determined based on the principal requested, the term of the loan, and the customer's home state. It then uses a mortgage calculator to calculate the ratio by dividing the potential monthly payment by the customer's income. The ratio and credit score are passed to do a risk assessment that makes the final decision (see Figure 2).

Using SCA To Implement the Mortgage Loan Approval Application
In the next sections we'll implement the loan approval application using SCA and walk through the creation of individual SCA artifacts. At a high level the loan approval application can be broken down into a number of SCA components that are assembled together into a composite. The components in this composite consist of Loan Approval, Credit Check, Interest Rate, Mortgage Calculator, and Risk Assessment components. The entire composite is deployed in a SCA system (see Figure 3).

SCA Components
An SCA component is the basic building block for creating SOA applications and is characterized by three distinct and yet related pieces of information: a) The program logic that provides the function of the building block (referred to as implementation), b) The definition of how this building block might interact with other components (referred to as component type) c) The concrete description of how this building block fits with all the other blocks to build a solution (referred to as assembly or composition). We'll explain each in more detail in the following sections and give examples but here's an overview.

  • Component Type: The component implementation is provided using any programming language that's supported by an SCA runtime. Component implementers are free to write in any style they're comfortable with but are bound by the services, references and properties, as defined by the component type, in the way that they interact with other SCA components. The SCA specifications describe how each programming language maps to SCA.
  • Component Type: Component type describes the shape of a component in terms of the services it exposes, the references it depends on and the properties that control the component's behavior. Component-type information can be found either in a file where, by convention, the name is ImplementationFileName.componentType and/or by introspection of the component implementation.
  • Component Composition/Assembly: Once a component's implementation and its component type are defined it's ready to be assembled into a network of services that together provide an SOA solution. The assembly is defined in an SCA composite file. The SCA runtime uses the information in this file to instantiate an SCA application.
SCA defines an XML format called Service Component Description Language (SCDL). SCDL is the XML format of component-type files and composite files. For example, the loan approval application's MortgageCalculator component has both component-type and component-implementation files and the MortgageCalculator component is described and wired together with other components in a composite file (see Figure 4).

Component Type
The MortgageCalculator component-type file (MortgageCalculator.componentType) describes the single service that components of this type provide. The MortgageCalculator component doesn't reference other components and doesn't provide any settable properties so <reference> and <property> elements don't appear.

<componentType>
    <service name="MortgageCalculatorService">
       <interface.java interface="mortgage.MortgageCalculator"/>
    </service>
</componentType>

Component Implementation
The class "mortgage.MortgageCalculatorImpl" (MortgageCalculatorImpl.java) contains the business logic for this component.

public class MortgageCalculatorImpl implements MortgageCalculator {
    public double getMonthlyPayment(double principal, int years, float interestRate) {
       double monthlyRate = interestRate / 12.0 / 100.0;
       double p = Math.pow(1 + monthlyRate, years * 12);
       double q = p / (p - 1);
       double monthlyPayment = principal * monthlyRate * q;
       return monthlyPayment;
    }
}

In the next section (Component Services) we show that if we chose to use annotations, as we can in the Java language, the component-type information can be included in the implementation file. Most of the code snippets in this paper use annotations to provide component-type information instead of using a component-type file.

Component Services
Let's take a look at how a component offers a service to others. In the following example MortgageCalculator exposes a service that contains one method, called getMonthlyPayment, by using a @Service annotation. As the Java language runtime supports annotations our method can be exposed as a service interface by simply annotating the class.

@Service(MortgageCalculator.class)
public class MortageCalculatorImpl implements MortageCalculator {

    public double getMonthlyPayment(double principal, float interestRate) {
       ...
    }
}

The @Service annotation tells the SCA runtime that the MortgageCalculatorImpl class instances are exposed as services with an interface defined by the MortgageCalculator interface.

Component References
Now let's look at how a component references other components. We'll use the Loan Approval component that references other components as our example here. Loan Approval is implemented using the Java language and will use annotations. It uses @Reference to indicate its dependency on RiskAssessment, CreditCheck, InterestRateQuote, and MortgageCalculator. The referenced components can be local or remote and the SCA runtime will ensure that these references are correctly set at runtime based on the wiring found in the completed application's SCDL files (shown later in this article). See Listing 1.

Component Interfaces
The business functions provided by a service or required by a reference are described using interfaces in SCA. The interfaces represent the contract for a service or reference. Java and WSDL are two typical interface definition languages.

@Remotable
public interface CreditCheck {
    int getCreditScore(String ssn);
}

Interfaces can be local or remotable. Local interfaces are the most optimized for local interactions between components in the same composite. In contrast, remotable interfaces can be used for loosely coupled remote interactions.

Some business services have peer-to-peer relationships that require a two-way dependency at the service level. In these cases, the business service represents both a consumer of a service provided by a partner business service and a provider of a service to the partner business service. This is especially the case when the interactions are based on asynchronous messaging rather than on remote procedure calls. SCA uses bi-directional interfaces to directly model peer-to-peer bi-directional business service relationships.

For some services a sequence of operations must be called to achieve some higher-level goal. The sequence of operations is referred to as conversation. If the service uses a bi-directional interface, the conversation may include both operations and callbacks. SCA allows interfaces to be marked as conversational to bracket the series of operations in the same conversation.

Component Properties
Component properties can be used to alter the behavior of a component at runtime without making code changes. Let's assume that the LoanApproval component has a component property called "minimumCreditScore," which can be set to different values based on company policy. Below is a code snippet from the LoanApproval component implementation that uses an @Property annotation to identify a property called minimumCreditScore. The property has a default value of 650:

private int minimumCreditScore = 650;

// Property declaration using a setter method
@Property(name = "minimumCreditScore", override = "may")
public void setMinimumCreditScore(int minimumCreditScore) {
    this.minimumCreditScore = minimumCreditScore;
}

The following illustrates customization of the component by setting the "minimumCreditScore" property to 600 in the composite SCDL file to override the default value (650) defined in the component type (remember that we're using Java language annotations to define the component type):

<component name="LoanApprovalComponent">
    <implementation.java class="mortgage.LoanApprovalImpl" />
    <property name="minimumCreditScore">600</property>
    ...
</component>

Composites - Composing Components
So far we've concentrated on developing individual components, making them available as services and defining their dependencies on other services. Now let's look at how the components can be assembled to provide a business solution. This is referred to as a composite, which is a logical concept. A composite contains one or more components (see Figure 5).

If we look at the composite file (default.scdl) for MortgageComposite we can see how this draws all of the components together.

The SCA runtime uses the information in this SCDL file to instantiate, assemble, and configure the components. As can be seen from the example each component is identified by a <component> element in the file and can have references to other components. In this example, LoanApprovalComponent has four <reference> elements that are wired to four other components in the composite. The wiring is depicted through arrows in the diagram. The interfaces on both sides of the wire have to be compatible.

A composite can be reused as a component in the assembly but we don't show an example in this article.

Local Services
The composite file we've just seen shows how component references are "wired" to other components. There's no information included in this composite file to describe what techniques should be used to pass messages between the components. In this case SCA assumes that the components will be local to one another, i.e., they'll be instantiated and run in the same process address space. As we're using the Java language in this example the component instances will run in the same Java VM. SCA is free in this case to use the most efficient mechanism for moving a message from one component to another. This is likely to be a direct component-to-component call with little or no mediation.

On the face of it composition of components using local wiring may not appear to be very useful. Why not simply code these components as normal Java classes and have them interact in the normal way? In the case of coarse-grain components SCA has a number of advantages.

  • Components can easily be reused and reconfigured in other compositions
  • Components that are local today can be made remote tomorrow
  • Components implemented using different supported programming languages can easily be assembled

More Stories By Haleh Mahbod

Haleh Mahbod is a program director with IBM, managing the team contributing to the Apache Tuscany as well as SOA for PHP open source. She has extensive development experience with database technologies and integration servers.

More Stories By Raymond Feng

Raymond Feng is a senior software engineer with IBM. He is now working on the Service Component Architecture (SCA) runtime implementation in Apache Tuscany project as a committer. Raymond has been developing SOA for more than 4 years and he was a key developer and team lead for WebSphere Process Server products since 2002.

More Stories By Simon Laws

Simon Laws is a member of the IBM Open Source SOA project team working with the open source Apache and PHP communities to build Java, C++, and PHP implementations of the Service Component Architecture (SCA) and Service Data Object (SDO) specifications. Prior to this role he was working in the distributed computing space building service-oriented solutions for customers with a particular interest in grid computing and virtualization.

Comments (1) View Comments

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.


Most Recent Comments
Stephan 01/23/07 05:11:58 PM EST

For people interested... you can find an SCA presentation (audio + sync'ed slides) by Michael Rowley (BEA) on Parleys.com ! Enjoy.

@ThingsExpo Stories
Software AG helps organizations transform into Digital Enterprises, so they can differentiate from competitors and better engage customers, partners and employees. Using the Software AG Suite, companies can close the gap between business and IT to create digital systems of differentiation that drive front-line agility. We offer four on-ramps to the Digital Enterprise: alignment through collaborative process analysis; transformation through portfolio management; agility through process automation and integration; and visibility through intelligent business operations and big data.
There will be 50 billion Internet connected devices by 2020. Today, every manufacturer has a propriety protocol and an app. How do we securely integrate these "things" into our lives and businesses in a way that we can easily control and manage? Even better, how do we integrate these "things" so that they control and manage each other so our lives become more convenient or our businesses become more profitable and/or safe? We have heard that the best interface is no interface. In his session at Internet of @ThingsExpo, Chris Matthieu, Co-Founder & CTO at Octoblu, Inc., will discuss how these devices generate enough data to learn our behaviors and simplify/improve our lives. What if we could connect everything to everything? I'm not only talking about connecting things to things but also systems, cloud services, and people. Add in a little machine learning and artificial intelligence and now we have something interesting...
Last week, while in San Francisco, I used the Uber app and service four times. All four experiences were great, although one of the drivers stopped for 30 seconds and then left as I was walking up to the car. He must have realized I was a blogger. None the less, the next car was just a minute away and I suffered no pain. In this article, my colleague, Ved Sen, Global Head, Advisory Services Social, Mobile and Sensors at Cognizant shares his experiences and insights.
We are reaching the end of the beginning with WebRTC and real systems using this technology have begun to appear. One challenge that faces every WebRTC deployment (in some form or another) is identity management. For example, if you have an existing service – possibly built on a variety of different PaaS/SaaS offerings – and you want to add real-time communications you are faced with a challenge relating to user management, authentication, authorization, and validation. Service providers will want to use their existing identities, but these will have credentials already that are (hopefully) irreversibly encoded. In his session at Internet of @ThingsExpo, Peter Dunkley, Technical Director at Acision, will look at how this identity problem can be solved and discuss ways to use existing web identities for real-time communication.
Can call centers hang up the phones for good? Intuitive Solutions did. WebRTC enabled this contact center provider to eliminate antiquated telephony and desktop phone infrastructure with a pure web-based solution, allowing them to expand beyond brick-and-mortar confines to a home-based agent model. It also ensured scalability and better service for customers, including MUY! Companies, one of the country's largest franchise restaurant companies with 232 Pizza Hut locations. This is one example of WebRTC adoption today, but the potential is limitless when powered by IoT. Attendees will learn real-world benefits of WebRTC and explore future possibilities, as WebRTC and IoT intersect to improve customer service.
From telemedicine to smart cars, digital homes and industrial monitoring, the explosive growth of IoT has created exciting new business opportunities for real time calls and messaging. In his session at Internet of @ThingsExpo, Ivelin Ivanov, CEO and Co-Founder of Telestax, will share some of the new revenue sources that IoT created for Restcomm – the open source telephony platform from Telestax. Ivelin Ivanov is a technology entrepreneur who founded Mobicents, an Open Source VoIP Platform, to help create, deploy, and manage applications integrating voice, video and data. He is the co-founder of TeleStax, an Open Source Cloud Communications company that helps the shift from legacy IN/SS7 telco networks to IP-based cloud comms. An early investor in multiple start-ups, he still finds time to code for his companies and contribute to open source projects.
The Internet of Things (IoT) promises to create new business models as significant as those that were inspired by the Internet and the smartphone 20 and 10 years ago. What business, social and practical implications will this phenomenon bring? That's the subject of "Monetizing the Internet of Things: Perspectives from the Front Lines," an e-book released today and available free of charge from Aria Systems, the leading innovator in recurring revenue management.
The Internet of Things will put IT to its ultimate test by creating infinite new opportunities to digitize products and services, generate and analyze new data to improve customer satisfaction, and discover new ways to gain a competitive advantage across nearly every industry. In order to help corporate business units to capitalize on the rapidly evolving IoT opportunities, IT must stand up to a new set of challenges.
There’s Big Data, then there’s really Big Data from the Internet of Things. IoT is evolving to include many data possibilities like new types of event, log and network data. The volumes are enormous, generating tens of billions of logs per day, which raise data challenges. Early IoT deployments are relying heavily on both the cloud and managed service providers to navigate these challenges. In her session at 6th Big Data Expo®, Hannah Smalltree, Director at Treasure Data, to discuss how IoT, Big Data and deployments are processing massive data volumes from wearables, utilities and other machines.
All major researchers estimate there will be tens of billions devices – computers, smartphones, tablets, and sensors – connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades. With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo in Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be!
P2P RTC will impact the landscape of communications, shifting from traditional telephony style communications models to OTT (Over-The-Top) cloud assisted & PaaS (Platform as a Service) communication services. The P2P shift will impact many areas of our lives, from mobile communication, human interactive web services, RTC and telephony infrastructure, user federation, security and privacy implications, business costs, and scalability. In his session at Internet of @ThingsExpo, Erik Lagerway, Co-founder of Hookflash, will walk through the shifting landscape of traditional telephone and voice services to the modern P2P RTC era of OTT cloud assisted services.
While great strides have been made relative to the video aspects of remote collaboration, audio technology has basically stagnated. Typically all audio is mixed to a single monaural stream and emanates from a single point, such as a speakerphone or a speaker associated with a video monitor. This leads to confusion and lack of understanding among participants especially regarding who is actually speaking. Spatial teleconferencing introduces the concept of acoustic spatial separation between conference participants in three dimensional space. This has been shown to significantly improve comprehension and conference efficiency.
The Internet of Things is tied together with a thin strand that is known as time. Coincidentally, at the core of nearly all data analytics is a timestamp. When working with time series data there are a few core principles that everyone should consider, especially across datasets where time is the common boundary. In his session at Internet of @ThingsExpo, Jim Scott, Director of Enterprise Strategy & Architecture at MapR Technologies, will discuss single-value, geo-spatial, and log time series data. By focusing on enterprise applications and the data center, he will use OpenTSDB as an example to explain some of these concepts including when to use different storage models.
SYS-CON Events announced today that Gridstore™, the leader in software-defined storage (SDS) purpose-built for Windows Servers and Hyper-V, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Gridstore™ is the leader in software-defined storage purpose built for virtualization that is designed to accelerate applications in virtualized environments. Using its patented Server-Side Virtual Controller™ Technology (SVCT) to eliminate the I/O blender effect and accelerate applications Gridstore delivers vmOptimized™ Storage that self-optimizes to each application or VM across both virtual and physical environments. Leveraging a grid architecture, Gridstore delivers the first end-to-end storage QoS to ensure the most important App or VM performance is never compromised. The storage grid, that uses Gridstore’s performance optimized nodes or capacity optimized nodes, starts with as few a...
The Transparent Cloud-computing Consortium (abbreviation: T-Cloud Consortium) will conduct research activities into changes in the computing model as a result of collaboration between "device" and "cloud" and the creation of new value and markets through organic data processing High speed and high quality networks, and dramatic improvements in computer processing capabilities, have greatly changed the nature of applications and made the storing and processing of data on the network commonplace. These technological reforms have not only changed computers and smartphones, but are also changing the data processing model for all information devices. In particular, in the area known as M2M (Machine-To-Machine), there are great expectations that information with a new type of value can be produced using a variety of devices and sensors saving/sharing data via the network and through large-scale cloud-type data processing. This consortium believes that attaching a huge number of devic...
Innodisk is a service-driven provider of industrial embedded flash and DRAM storage products and technologies, with a focus on the enterprise, industrial, aerospace, and defense industries. Innodisk is dedicated to serving their customers and business partners. Quality is vitally important when it comes to industrial embedded flash and DRAM storage products. That’s why Innodisk manufactures all of their products in their own purpose-built memory production facility. In fact, they designed and built their production center to maximize manufacturing efficiency and guarantee the highest quality of our products.
All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades. Over the summer Gartner released its much anticipated annual Hype Cycle report and the big news is that Internet of Things has now replaced Big Data as the most hyped technology. Indeed, we're hearing more and more about this fascinating new technological paradigm. Every other IT news item seems to be about IoT and its implications on the future of digital business.
Can call centers hang up the phones for good? Intuitive Solutions did. WebRTC enabled this contact center provider to eliminate antiquated telephony and desktop phone infrastructure with a pure web-based solution, allowing them to expand beyond brick-and-mortar confines to a home-based agent model. Download Slide Deck: ▸ Here
BSQUARE is a global leader of embedded software solutions. We enable smart connected systems at the device level and beyond that millions use every day and provide actionable data solutions for the growing Internet of Things (IoT) market. We empower our world-class customers with our products, services and solutions to achieve innovation and success. For more information, visit www.bsquare.com.
With the iCloud scandal seemingly in its past, Apple announced new iPhones, updates to iPad and MacBook as well as news on OSX Yosemite. Although consumers will have to wait to get their hands on some of that new stuff, what they can get is the latest release of iOS 8 that Apple made available for most in-market iPhones and iPads. Originally announced at WWDC (Apple’s annual developers conference) in June, iOS 8 seems to spearhead Apple’s newfound focus upon greater integration of their products into everyday tasks, cross-platform mobility and self-monitoring. Before you update your device, here is a look at some of the new features and things you may want to consider from a mobile security perspective.