Microservices Expo Authors: Stackify Blog, Elizabeth White, Pat Romanski, Liz McMillan, Yeshim Deniz

Related Topics: Java IoT

Java IoT: 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).

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.

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

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.

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.

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>

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.

@MicroservicesExpo Stories
It has never been a better time to be a developer! Thanks to cloud computing, deploying our applications is much easier than it used to be. How we deploy our apps continues to evolve thanks to cloud hosting, Platform-as-a-Service (PaaS), and now Function-as-a-Service. FaaS is the concept of serverless computing via serverless architectures. Software developers can leverage this to deploy an individual "function", action, or piece of business logic. They are expected to start within milliseconds...
Most DevOps journeys involve several phases of maturity. Research shows that the inflection point where organizations begin to see maximum value is when they implement tight integration deploying their code to their infrastructure. Success at this level is the last barrier to at-will deployment. Storage, for instance, is more capable than where we read and write data. In his session at @DevOpsSummit at 20th Cloud Expo, Josh Atwell, a Developer Advocate for NetApp, will discuss the role and value...
You know you need the cloud, but you’re hesitant to simply dump everything at Amazon since you know that not all workloads are suitable for cloud. You know that you want the kind of ease of use and scalability that you get with public cloud, but your applications are architected in a way that makes the public cloud a non-starter. You’re looking at private cloud solutions based on hyperconverged infrastructure, but you’re concerned with the limits inherent in those technologies.
Regardless of what business you’re in, it’s increasingly a software-driven business. Consumers’ rising expectations for connected digital and physical experiences are driving what some are calling the "Customer Experience Challenge.” In his session at @DevOpsSummit at 20th Cloud Expo, Marco Morales, Director of Global Solutions at CollabNet, will discuss how organizations are increasingly adopting a discipline of Value Stream Mapping to ensure that the software they are producing is poised to o...
DevOps at Cloud Expo – being held October 31 - November 2, 2017, 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 world's largest enterprises – and delivering real r...
Cloud promises the agility required by today’s digital businesses. As organizations adopt cloud based infrastructures and services, their IT resources become increasingly dynamic and hybrid in nature. Managing these require modern IT operations and tools. In his session at 20th Cloud Expo, Raj Sundaram, Senior Principal Product Manager at CA Technologies, will discuss how to modernize your IT operations in order to proactively manage your hybrid cloud and IT environments. He will be sharing bes...
SYS-CON Events announced today that CollabNet, a global leader in enterprise software development, release automation and DevOps solutions, will be a Bronze Sponsor of SYS-CON's 20th International Cloud Expo®, taking place from June 6-8, 2017, at the Javits Center in New York City, NY. CollabNet offers a broad range of solutions with the mission of helping modern organizations deliver quality software at speed. The company’s latest innovation, the DevOps Lifecycle Manager (DLM), supports Value S...
SYS-CON Events announced today that Peak 10, Inc., a national IT infrastructure and cloud services provider, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Peak 10 provides reliable, tailored data center and network services, cloud and managed services. Its solutions are designed to scale and adapt to customers’ changing business needs, enabling them to lower costs, improve performance and focus intern...
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm. In his Day 3 Keynote at 20th Cloud Expo, Chris Brown, a Solutions Marketing Manager at Nutanix, will explore t...
This talk centers around how to automate best practices in a multi-/hybrid-cloud world based on our work with customers like GE, Discovery Communications and Fannie Mae. Today’s enterprises are reaping the benefits of cloud computing, but also discovering many risks and challenges. In the age of DevOps and the decentralization of IT, it’s easy to over-provision resources, forget that instances are running, or unintentionally expose vulnerabilities.
There are two main reasons for infrastructure automation. First, system administrators, IT professionals and DevOps engineers need to automate as many routine tasks as possible. That’s why we build tools at Stackify to help developers automate processes like application performance management, error monitoring, and log management; automation means you have more time for mission-critical tasks. Second, automation makes the management of complex, diverse environments possible and allows rapid scal...
One of the biggest challenges with adopting a DevOps mentality is: new applications are easily adapted to cloud-native, microservice-based, or containerized architectures - they can be built for them - but old applications need complex refactoring. On the other hand, these new technologies can require relearning or adapting new, oftentimes more complex, methodologies and tools to be ready for production. In his general session at @DevOpsSummit at 20th Cloud Expo, Chris Brown, Solutions Marketi...
We all know that end users experience the internet primarily with mobile devices. From an app development perspective, we know that successfully responding to the needs of mobile customers depends on rapid DevOps – failing fast, in short, until the right solution evolves in your customers' relationship to your business. Whether you’re decomposing an SOA monolith, or developing a new application cloud natively, it’s not a question of using microservices - not doing so will be a path to eventual ...
SYS-CON Events announced today that Linux Academy, the foremost online Linux and cloud training platform and community, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Linux Academy was founded on the belief that providing high-quality, in-depth training should be available at an affordable price. Industry leaders in quality training, provided services, and student certification passes, its goal is to c...
SYS-CON Events announced today that Fusion, a leading provider of cloud services, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry’s single source for the cloud. Fusion’s advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including cloud...
SYS-CON Events announced today that HTBase will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. HTBase (Gartner 2016 Cool Vendor) delivers a Composable IT infrastructure solution architected for agility and increased efficiency. It turns compute, storage, and fabric into fluid pools of resources that are easily composed and re-composed to meet each application’s needs. With HTBase, companies can quickly prov...
@DevOpsSummit at Cloud taking place June 6-8, 2017, at Javits Center, New York City, is co-located with the 20th International 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 developm...
With 10 simultaneous tracks, keynotes, general sessions and targeted breakout classes, Cloud Expo and @ThingsExpo are two of the most important technology events of the year. Since its launch over eight years ago, Cloud Expo and @ThingsExpo have presented a rock star faculty as well as showcased hundreds of sponsors and exhibitors! In this blog post, I provide 7 tips on how, as part of our world-class faculty, you can deliver one of the most popular sessions at our events. But before reading the...
The purpose of this article is draw attention to key SaaS services that are commonly overlooked during contact signing that are essential to ensuring they meet the expectations and requirements of the organization and provide guidance and recommendations for process and controls necessary for achieving quality SaaS contractual agreements.
SYS-CON Events announced today that OpsGenie will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Founded in 2012, OpsGenie is an alerting and on-call management solution for dev and ops teams. OpsGenie provides the tools needed to design actionable alerts, manage on-call schedules and escalations, and ensure that the right people are notified at the right time, using multiple notification methods.