Welcome!

SOA & WOA Authors: Miguel Valdes Faura, Liz McMillan, Yeshim Deniz, Plutora Blog, Pat Romanski

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
Since 2008 and for the first time in history, more than half of humans live in urban areas, urging cities to become “smart.” Today, cities can leverage the wide availability of smartphones combined with new technologies such as Beacons or NFC to connect their urban furniture and environment to create citizen-first services that improve transportation, way-finding and information delivery. In her session at @ThingsExpo, Laetitia Gazel-Anthoine, CEO of Connecthings, will focus on successful use cases.
The industrial software market has treated data with the mentality of “collect everything now, worry about how to use it later.” We now find ourselves buried in data, with the pervasive connectivity of the (Industrial) Internet of Things only piling on more numbers. There’s too much data and not enough information. In his session at @ThingsExpo, Bob Gates, Global Marketing Director, GE’s Intelligent Platforms business, to discuss how realizing the power of IoT, software developers are now focused on understanding how industrial data can create intelligence for industrial operations. Imagine ...
Things are being built upon cloud foundations to transform organizations. This CEO Power Panel at 15th Cloud Expo, moderated by Roger Strukhoff, Cloud Expo and @ThingsExpo conference chair, addressed the big issues involving these technologies and, more important, the results they will achieve. Rodney Rogers, chairman and CEO of Virtustream; Brendan O'Brien, co-founder of Aria Systems, Bart Copeland, president and CEO of ActiveState Software; Jim Cowie, chief scientist at Dyn; Dave Wagstaff, VP and chief architect at BSQUARE Corporation; Seth Proctor, CTO of NuoDB, Inc.; and Andris Gailitis, C...
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
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, discussed 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 t...
Cultural, regulatory, environmental, political and economic (CREPE) conditions over the past decade are creating cross-industry solution spaces that require processes and technologies from both the Internet of Things (IoT), and Data Management and Analytics (DMA). These solution spaces are evolving into Sensor Analytics Ecosystems (SAE) that represent significant new opportunities for organizations of all types. Public Utilities throughout the world, providing electricity, natural gas and water, are pursuing SmartGrid initiatives that represent one of the more mature examples of SAE. We have s...
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
SYS-CON Media announced that Splunk, a provider of the leading software platform for real-time Operational Intelligence, has launched an ad campaign on Big Data Journal. Splunk software and cloud services enable organizations to search, monitor, analyze and visualize machine-generated big data coming from websites, applications, servers, networks, sensors and mobile devices. The ads focus on delivering ROI - how improved uptime delivered $6M in annual ROI, improving customer operations by mining large volumes of unstructured data, and how data tracking delivers uptime when it matters most.
The true value of the Internet of Things (IoT) lies not just in the data, but through the services that protect the data, perform the analysis and present findings in a usable way. With many IoT elements rooted in traditional IT components, Big Data and IoT isn’t just a play for enterprise. In fact, the IoT presents SMBs with the prospect of launching entirely new activities and exploring innovative areas. CompTIA research identifies several areas where IoT is expected to have the greatest impact.
There is no doubt that Big Data is here and getting bigger every day. Building a Big Data infrastructure today is no easy task. There are an enormous number of choices for database engines and technologies. To make things even more challenging, requirements are getting more sophisticated, and the standard paradigm of supporting historical analytics queries is often just one facet of what is needed. As Big Data growth continues, organizations are demanding real-time access to data, allowing immediate and actionable interpretation of events as they happen. Another aspect concerns how to deliver ...
The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, discussed how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money!
Scott Jenson leads a project called The Physical Web within the Chrome team at Google. Project members are working to take the scalability and openness of the web and use it to talk to the exponentially exploding range of smart devices. Nearly every company today working on the IoT comes up with the same basic solution: use my server and you'll be fine. But if we really believe there will be trillions of these devices, that just can't scale. We need a system that is open a scalable and by using the URL as a basic building block, we open this up and get the same resilience that the web enjoys.
Code Halos - aka "digital fingerprints" - are the key organizing principle to understand a) how dumb things become smart and b) how to monetize this dynamic. In his session at @ThingsExpo, Robert Brown, AVP, Center for the Future of Work at Cognizant Technology Solutions, outlined research, analysis and recommendations from his recently published book on this phenomena on the way leading edge organizations like GE and Disney are unlocking the Internet of Things opportunity and what steps your organization should be taking to position itself for the next platform of digital competition.
In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect at GE, and Ibrahim Gokcen, who leads GE's advanced IoT analytics, focused on the Internet of Things / Industrial Internet and how to make it operational for business end-users. Learn about the challenges posed by machine and sensor data and how to marry it with enterprise data. They also discussed the tips and tricks to provide the Industrial Internet as an end-user consumable service using Big Data Analytics and Industrial Cloud.
How do APIs and IoT relate? The answer is not as simple as merely adding an API on top of a dumb device, but rather about understanding the architectural patterns for implementing an IoT fabric. There are typically two or three trends: Exposing the device to a management framework Exposing that management framework to a business centric logic Exposing that business layer and data to end users. This last trend is the IoT stack, which involves a new shift in the separation of what stuff happens, where data lives and where the interface lies. For instance, it's a mix of architectural styles ...
IoT is still a vague buzzword for many people. In his session at @ThingsExpo, Mike Kavis, Vice President & Principal Cloud Architect at Cloud Technology Partners, discussed the business value of IoT that goes far beyond the general public's perception that IoT is all about wearables and home consumer services. He also discussed how IoT is perceived by investors and how venture capitalist access this space. Other topics discussed were barriers to success, what is new, what is old, and what the future may hold. Mike Kavis is Vice President & Principal Cloud Architect at Cloud Technology Pa...
Dale Kim is the Director of Industry Solutions at MapR. His background includes a variety of technical and management roles at information technology companies. While his experience includes work with relational databases, much of his career pertains to non-relational data in the areas of search, content management, and NoSQL, and includes senior roles in technical marketing, sales engineering, and support engineering. Dale holds an MBA from Santa Clara University, and a BA in Computer Science from the University of California, Berkeley.
The Internet of Things (IoT) is rapidly in the process of breaking from its heretofore relatively obscure enterprise applications (such as plant floor control and supply chain management) and going mainstream into the consumer space. More and more creative folks are interconnecting everyday products such as household items, mobile devices, appliances and cars, and unleashing new and imaginative scenarios. We are seeing a lot of excitement around applications in home automation, personal fitness, and in-car entertainment and this excitement will bleed into other areas. On the commercial side, m...
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity.
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.