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Ivano Malavolta
Modern development paradigms
Roadmap
Software product-lines
Service-oriented architecture
Software product-lines
An Example
You are constructing software that supports a bank loan office There are 20 products in your product line An existing module calculates customer interest payment
– Perfectly adequate for 19 of the products – Needs 240 lines modification for Delaware
How to Manage the Modifications?
One strategy is to make another copy of the affected module and insert the necessary changes
– Called “clone and own” – Fast and easy – Does not scale!
• Suppose each of the 20 products has 1000 modules • Potentially huge number of distinct versions of the product to maintain
A better strategy is to introduce a “variation point” in the module and manage the variation point with, e.g., a configuration parameter
– Setting configuration parameter to “normal” will generate the 18 products as before
– Setting the configuration parameter to “Delaware” will generate the new version specifically for Delaware
Product lines
A set of related products that have substantial commonality – In general, the commonality exists at the architecture level
One potential ‘silver bullet’ of software engineering – Power through reuse of
• Engineering knowledge • Existing product architectures, styles, patterns • Pre-existing software components and connectors
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Traditional Software Engineering
Business motivation for product lines
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Traditional Software Engineering
Business motivation for product lines
Product-line-based engineering
Business motivation for product lines
The ROI of SPL
David M. Weiss and Chi Tau Robert Lai. 1999. Software Product-Line Engineering: A Family-Based Software Development Process. Addison-Wesley Longman Publishing Co., Inc., Boston, MA, USA.
SPL engineering
Conceptual framework of PLs
Image © Paolo Ciancarini
Assets DEF: artifacts that are representable with software and either compose a product or support the engineering process to create a product Reuse in general needs to be planned for being
– Reusable: • is fully documented • is verified independently with high confidence
– Usable: • is adaptable and that is usable in a variety of situations
Design for reuse/use involves – analysis to identify explicitly variations to anticipate adaptations – design for adaptability, engineered a
priori to create assets for future developments
Examples of assets
• requirements • design specifications • design models • source code • build files • test plans and test cases • user documentation • repair manuals and installation guides • project budgets, schedules, and work plans • product calibration and configuration files • data models and parts lists • …
Capturing product line architectures
• Common: features common to all products • A: features specific to product A • B: features specific to product B • Product A = Common + A • Product B = Common + B 15
B
A
B
Common
A
Common
A
Common
B
(a) (b) (c)
Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; (C) 2008 John Wiley & Sons, Inc. Reprinted with permission.
A product-line architecture
Definition A product-line architecture captures the architectures of many related products simultaneously
Generally employs explicit variation points in the architecture indicating where design decisions may diverge from product to product
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“Lite” “Demo” “Pro”
A lunar lander product line
Product component table
Helps us decide whether creating a product line is viable or feasible
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Group components into features
Not a mechanical process Attempt to identify (mostly) orthogonal features, or features that would be beneficial in different products
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Reconstitute products from features
Use technical and business knowledge to identify which combinations form feasible or marketable products that will be constructed
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Lunar Lander Pro X X
How to represent variability?
1. Integrated variability modeling – variability concepts are introduced into existing modelling
languages or document templates
2. Orthogonal variability modeling – Ad-hoc models for variability representation
• called feature models • separated from architectural models • reusable independently from the used ALs • understandable by non-technical stakeholders
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1 - Integrated variability modeling
Architectural models need to be diversified with information about variation points and features Not all ALs have good support for this
– Exceptions include • Koala • xADL 2.0
– These ALs have explicit support for capturing variation points
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2 – Orthogonal variability modeling
The variability of the product line is treated as a first class product line artifact à the feature model
Note that commonalities are not represented here
Concepts
Variation point
– a variable item and thus defines “what can vary” (without saying how it can vary)
Variant
– a concrete variation – is related to a variation point
Variability constraints
– restrictions about the variability – e.g.
• to define permissible combinations of variants in an application • to define that the selection of one variant requires or excludes the selection of another variant
Feature model in the automotive domain
Exemplar of Automotive Architecture with Variability. Kacper Bak , Marko Novakovic , Leonardo Passos. Technical report.
Product-line selection is the process of extracting a single product architecture (or smaller product line) from an architectural model that contains explicit points of variation ALs such as Koala and xADL 2.0 can do selection automatically with tools
Uses: product lines for feature selection
Products in a product line don’t have to exclusively capture alternatives
– They can also capture variation over time
Uses: product lines for evolution
Uses: product lines for evolution
Uses: product lines for ‘what-if’ analysis
In addition to alternative products and different versions of the same product, product lines can capture different potential products
– Selection can be used to quickly generate product architectures for potential products
– These can be checked for certain properties or subjected to more rigorous analysis for feasibility or quality
– Can also be used to generate new product ideas
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Implementation issues
Important to partition implementations along variation-point boundaries
Common
File1.java
File2.java
File3.java
File4.java
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B
Common
File1.java
File2.java
File3.java
File4.java
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(a) (b)Bad Good
Implementation issues 2
Keeping evolving architectures and version-controlled source repositories (e.g., Git, SVN) in sync
Text-Based UIComponent
Graphical UIComponent
1.0
2.0
3.0 2.1
4.0 2.2
Text-basedEvolution
GraphicalFork
UI.java(as versioned in a software
configuration management system)
Unifying products with different heritage Often, the idea to create a product line emerges after several products have been implemented and commonality is noticed Strategies include
– No product line • It may be more expensive to create a product line or there may
not be enough commonality – One master product
• One product architecture becomes the basis for the product line
– Hybrid • A new product line architecture emerges out of many products • Seems ideal but can be hard in practice
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Product lines in their context
Architectural Styles – Can be general or domain-specific – Provides general guidelines for diverse kinds of applications – Focus on –ility development
Domain-specific software architectures – Domain specific – Includes elaborate domain model and specific reference
architecture
Product lines – Explicit set of related products with common aspects
Style DSSA / Ref Arch Product Line
Example: lunar lander in Koala
• No product line features yet
interface IDataStore{ void setAltitude(int altitudeInMeters); int getAltitude(); void setBurnRate(int newBurnRate); int getBurnRate(); ... }
Example: lunar lander PL in Koala
• Switch construct routes calls to one of two potential data stores
• ‘Diversity interface’ lets game logic component select callee from external config component
• Same IDataStore interface ensures call compatibility
Example 2: SPL for robotics
L. Gherardi, “Variability modeling and resolution in component-based robotics systems,” PhD Thesis, 2013.
Example 2: SPL for robotics
L. Gherardi, “Variability modeling and resolution in component-based robotics systems,” PhD Thesis, 2013.
Open research challenges in variability modeling and analysis • Variability modelling
– Understanding tradeoffs between expressiveness and analyzability – Interrelating variability with base models – Handling large-scale variability models
• Variability analysis – Metrics for performance of solvers prediction – Large-scale, realistic variability models for empirical studies
• Product management – Scope optimization – Artifact-interrelations in multi-level product lines
Open research challenges in domain engineering • Domain requirements engineering
– Interrelation between scoping and requirements engineering – Interrelation between requirements engineering and other
development activities – Impact of requirements changes
• Domain design – Building resilient service-oriented product lines – Delayed design decision and variability – SPLE and cloud computing – Variability in quality attributes
• Domain realization – Mapping of product line variability and software variability
Open research challenges in domain engineering 2 • Quality assurance
– Causes for failures – Inter-model verification – Empirical evidence – Empowering additional quality assurance techniques during
domain engineering
Open research challenges in application engineering • Application requirements engineering
– ︎Eliciting application-specific requirements – Handling application-specific deviations
• Application design – ︎Documentation of application design alternatives – Impact of application-specific extensions
• Application realization – Framing application-specific programming – Extended configuration mechanism – Product line development environments
Open research challenges in application engineering • Application quality assurance
– Minimizing test redundancy – Correct variability bindings – Empowering additional quality assurance techniques – Empirical evidence
• Variability management in non-product-line settings • Leveraging instantaneous feedback • Open world assumption
– Exploration of autonomic computing principles – Reasoning in the presence of variability and uncertainty – Human-in-the-loop adaptations – Run-time quality assurance
Service-oriented architecture
Introduction to service orientation
Three individuals, each capable of providing a distinct service
Introduction to service orientation
A company that employs these three people can compose their capabilities to carry out its business
Services are collections of capabilities
Much like a human, an automated service can provide multiple capabilities Public capabilities are commonly expressed via a published service contract (much like a traditional API)
Service composition
A service composition is a coordinated aggregate of services The functional context of each service is agnostic to any business process à services can participate in multiple service compositions à reusability + testability
MASHUP When data and information from various sources integrated in order to provide new features and services on a single graphical interface
Data
Web services
RSS feed
Platform APIs Mashup
application
Single graphical interface
Basic example of service composition
Basic example of service composition
Services inventory Establishes a pool of services, many of which will be deliberately designed to be reused within multiple service compositions
SOA principles
1. Standardized service contract 2. Service loose coupling 3. Service abstraction 4. Service reusability 5. Service autonomy 6. Service statelessness 7. Service discoverability 8. Service composability
1 - Standardized service contract Services within the same service inventory are in compliance with the same contract design standards “contract first” approach
2 - Service loose coupling
Service contracts are decoupled from their surrounding environment The service contract be the sole means of accessing service logic and resources
3 - Service abstraction
Service contracts contain only essential information Information about services is limited to what is published in service contracts Consumers may be unaware that a service is composing others
4 - Service reusability Services contain and express agnostic logic Services can be positioned as reusable enterprise resources
5 - Service autonomy Services exercise a high level of control over their underlying runtime execution environment Reducing shared access to service resources and increasing physical isolation can raise a service's ability to function autonomously
6 - Service statelessness Services minimize resource consumption by deferring the management of state information when necessary State data management consumes system resources and can result in a significant resource burden when multiple instances of services are concurrently invoked
7 - Service discoverability Services are supplemented with communicative metadata by which they can be effectively discovered and interpreted It enables a wide range of project team members to effectively carry out the discovery process and not to limit it to those with technical expertise
8 - Service composability Services can be repurposed to solve multiple problems à services must address agnostic or cross-cutting concerns
Notice that capabilities are composed within a service composition, not services
Summary
Service-oriented architecture
A means of developing distributed systems where the components are stand-alone services
Services may execute on different computers from different service providers
Standard protocols have been developed to support service communication and information exchange
Service-oriented architecture
Serviceregistry
Servicerequestor
Serviceprovider
Service
Find Publish
Bind (SOAP)(WSDL)
Benefits of SOA
• Services can be provided locally or outsourced to external providers
• Services are language-independent • Investment in legacy systems can be preserved • Inter-organisational computing is facilitated through
simplified information exchange
Key standards
• SOAP – A message exchange standard that supports service
communication
• WSDL (Web Service Definition Language) – To define a service interface and its bindings
• WS-BPEL – A standard for workflow languages used to define service
composition
Web service standards
Transport (HTTP, HTTPS, SMTP, ...)
Messaging (SOAP)
Service definition (UDDI, WSDL)
Process (WS-BPEL)
Support (WS-Security, WS-Addressing, ...)
XML technologies (XML, XSD, XSLT, ....)
RESTful web services
Current web services standards have been criticized as ‘heavyweight’ standards that are over-general and inefficient REST (REpresentational State Transfer) is an architectural style based on transferring representations of resources from a server to a client
– This style underlies the web as a whole and is simpler than SOAP/WSDL for implementing web services
– RESTFul services involve a lower overhead
We will have a seminar on REST in the next weeks
Example: in-car information system
1. Provides drivers with information on weather, road traffic conditions, local information etc.
2. It is linked to car radio so that information is delivered as a signal on a specific radio channel
3. The car is equipped with GPS receiver to discover its position and, based on that position, the system accesses a range of information services
4. Information may be delivered in the driver’s specified language
Example: in-car information system
User interface
Locator
Discovers carposition
Weatherinfo
Receives requestfrom user
Receiver
Receivesinformation stream
from services
Transmitter
Sends position andinformation request
to services
Radio
Translates digitalinfo stream toradio signal
In-car software system
Mobile Info Service
Facilitiesinfo
Translator
Roadlocator
Trafficinfo
Collates information
Road traffic info
commandgps coord
gpscoord gps coordgps coord
LanguageinfoInfo
stream
Service discovery
Finds availableservices
Advantage of SOA for this application
It is not necessary to decide when the system is programmed or deployed what service provider should be used or what specific services should be accessed
– As the car moves around, the in-car software uses the service discovery service to find the most appropriate information service and binds to that
– Because of the use of a translation service, it can move across borders and therefore make local information available to people who don’t speak the local language
Services as reusable components
• A service can be defined as: – A loosely-coupled, reusable software component that
encapsulates discrete functionality which may be distributed and programmatically accessed.
– A web service is a service that is accessed using standard Internet and XML-based protocols
Services are independent
– Services do not have a ‘requires’ interface – Services rely on message-based communication with messages
expressed in XML
SOA VS
component-based systems
WSDL: Web Service Description Language The service interface can be defined in a service description expressed in WSDL (Web Service Description Language)
• The WSDL specification defines – what operations the service supports – the format of the messages that are sent and received by the
service – how the service is accessed
• the binding between the abstract interface and the concrete set of protocols
– where the service is located • This is usually expressed as a URI (Universal Resource Identifier)
Organization of a WSDL specification
Intro
Abstract interface
Concreteimplementation
WSDL service definition
XML namespace declarations
Type declarationsInterface declarationsMessage declarations
Binding declarationsEndpoint declarations
Part of a WSDL description for a web service
Define some of the types used. Assume that the namespace prefixes ‘ws’ refers to the namespace URI for XML schemas and the namespace prefix associated with this definition is weathns. <types>
<xs: schema targetNameSpace = “http://.../weathns” xmlns: weathns = “http://…/weathns” > <xs:element name = “PlaceAndDate” type = “pdrec” /> <xs:element name = “MaxMinTemp” type = “mmtrec” /> <xs: element name = “InDataFault” type = “errmess” /> <xs: complexType name = “pdrec” <xs: sequence> <xs:element name = “town” type = “xs:string”/> <xs:element name = “country” type = “xs:string”/> <xs:element name = “day” type = “xs:date” /> </xs:complexType> Definitions of MaxMinType and InDataFault here
</schema> </types>
Part of a WSDL description for a web service
Now define the interface and its operations. In this case, there is only a single operation to return maximum and minimum temperatures. <interface name = “weatherInfo” >
<operation name = “getMaxMinTemps” pattern = “wsdlns: in-out”> <input messageLabel = “In” element = “weathns: PlaceAndDate” /> <output messageLabel = “Out” element = “weathns:MaxMinTemp” /> <outfault messageLabel = “Out” element = “weathns:InDataFault” />
</operation> </interface>
What this lecture means to you?
• Software product lines exploit the commonalities of a family of systems and systematically handle their variations
• Commonality is a property shared by all applications of the family – e.g., all mobile phones allow users to make calls
• Product line applications may differ in terms of features, functional and quality requirements they fulfill – e.g., some tablet computers may include mobile broadband connectivity,
others not
• Service-oriented software engineering is based on the notion that
programs can be constructed by composing independent services which encapsulate reusable functionality
• Service interfaces can be defined in WSDL – A WSDL specification includes a definition of the interface types and operations, the
binding protocol used by the service and the service location
References
Andreas Metzger and Klaus Pohl. 2014. Software product l ine engineering and variabil ity management: achievements and challenges. In Proceedings of the on Future of Software Engineering (FOSE 2014). ACM, New York, NY, USA, 70-84.
Contact Ivano Malavolta |
Post-doc researcher Gran Sasso Science Institute
iivanoo
www.ivanomalavolta.com
