P4L1 Components

Components Pieces that we put together "A component is an executable unit of independent production, acquisition, and deployment that can be composed into 3 functioning subsystem" - Clemens Szyperski Below are some business factors to tske into consideration when deciding whether to buy a software component from a third-party vendor. For each, determine whether that factor is enhanced or diminished if you decide to buy. Put 8 ‘+" next to factors that are benefitted and 38 ‘-’ next to factors that are diminished. — | Your uniqueness with respect to your competitors of which the component is a8 part 4+ | The amount of staff time required to develop the product + Your overdl production Ccosts = | Your control of the development process

e Buiding means in-house, Build Build Advantages and Disadvantages custom development - Costs more due to economy of scale + Tailored to specific situation » The advantages and disadvantages mirror those of buying The Third Way Use third-party components that can be customized during 3ssembly + Retain control of intellectual property In addition to buying complete applications or components, there are severd other ways that third parties can provide computational resources to 8 client. Match the examples in column 1 with the category in column 2: D A. PThreads B. NIST Time Service C. Tom-Tom GPS D. Checkstyle | [IN|| &+ E. PHP 1. Open source software 2. Turn-key equipment 3. IDE plugins 4. Cloud-based services 5. Software libraries

WordPress is 8 content management solution for blogs. Here are some requirements taeken from the WordPress codex. For each requirement, determine whether it concerns (3) component syntax; (b) component semantics; or (c) component composition: h | 1 Any text output by the [Action] function wil appear in the page source 3t the location where the action was invoked d | 2. Use wel-structured, error-free PHP and valid HTML - | 3- Actions are triggered by specific events in WordPress, such as publishing a8 post, changing themes, or displaying an administration screen. Action is 3 custom PHP function defined in your plugin and hooked to some of these events Examples of Component Models o SUN/Oracle Enterprise Java Beans (EJB). JQ2)EE, JSP (Java Server Pages) e Microsoft COM (Component Object Model). DCOM (Distributed COM), OLE (Object Linking and Embedding), ActiveX (web controls), COM+ (transactions) e Microsoft NET: CLI (Common Language Infrastructure), CLR (Runtime), ASPNET o CORBA Component Model (CCM). CORBA (Common Object Request Broker) from OMG:; Object Management Architecture (OMA), Interface Definition Language (IDL) » Web services: Web Services Description Language (WSDL), Universal Description, Discover, Innovation (UDDI), Simple Object Access Protocol (SOAP)

Issues 1. Configuration 2. Versioning 3. Extensions 4. Callbacks 5. Contracts 6. Objects as Components %. Scaling 8 . Domain Standards 1. Configuration o Components are typically configurable e Component vendors provide 3 means by which the client can tailor it to a particular situation e The flexibility that configuration gives comes at 3 cost

What are some of the third-party components that automobile manufacturers rely on? Write your answer in the text box: - Tires - Brakes - Battery - Muffler - Fluids 3. Extensions Components are often extended by adding new features « Singleton extension e Paralel extension of multiple components in the same dimension e Non-orthogonal extensions e Recursive extension

4. Callbacks Invariants e modules in 8 system are responsible for maintaining invariants « An operation provided by the client e Powerful tool that components can use for interacting with clients » presence of calbacks makes invariant maintenance much more difficult e But system integrity may be compromised during the * there is 3@ danger that the ~ time in which the client is in| client may do something . control that breaks the invariant Consider this sequence diagram describing 8 typical calback situation in which 8 Component captures 3 user event and invokes 3 client method via 3 callback. The Component is subject to corruption during which time period? Client Component O periOd from A to B . Client registers callback with Component> . B <User action captured by O period from B to C Eeoneit c - . —— . Callback invoked in Client O period from C to D > Callback invokes method in Client ® period from D to E - |l Component method returns O pe”Od from E to F E Callback returns >

Correctness Contracts e Pre and post conditions are specified for al caliable operations thus guaranteeing that component operations successfully execute I /{ Bl < OCLis a good candidate Collaboration Contracts e Interactions are specified, addressing issues such 3as synchronization, liveness and deadlock o Set of alowed interactions for 3 component that comprise that component’s protocol

Quality of Service Contracts e Non-functional requirements are 3addressed such as: Availability, Mean Time Between Failures, Mean Time to Repair, throughput, latency, data integrity, and capacity Consider the folowing snippets taken from the Oracle documentation of the format method in the Java PrintStream class. Classify each snippet with 8 Beugnard guarantee level (1 - Signature, 2 - Correctness, 3 - Coliaboration, and 4 - Quality of Service) in the corresponding text boxes: 3 | A Date formats are not synchronized. It is recommended [that you] create separate format instances for each thread. ' multiple threads access 8 format concurrently, [they] must be synchronized externaly 1 Biapublic Pri)ntStream format (Locale 1, String format, Object.. args 2 C. f a format string contains ilegal syntax, 8 format sSpecifier that is incompatible with the given arguments, insufficient arguments given the format string, or other ilegal conditions, then llegaFormatException is thrown Summary of Contracts The customer needs to know what he or she is getting

The "Fragile Base Class" Problem This occurs when 3 new version of 3 component \ changes one of its base \\ classes #. Scaling e Accounting e Deployment and configuration » Disputes e Quality of service e Fault containment and error handiing

8. Domain standards o there is tension between proprietary solutions and open standards o community benefits from standard solutions o standards take 3 long time h for approval and penetration For each of the technologies below enter p for proprietary technology and d for domain standard: HTML Direct3D UNIX OpenGL Java Javascript o.'oo.‘o'o"o.

Comparison of Differences \ Target Environments COM servers, Clents/desktops CORBA J2EE Servers * Development Environments NET . (2)EE | WebSphere (eClipse) Protocols Java IOP, XML, RM CLR | DCOM XML, SOAP COM | DCOM CORBA| 0P, XML

Comparison of Supported Variability e Java and CLI - singe VM for al platforms « COM - many languages, but Microsoft platforms only « CORBA - many languages, but each requires an DL binding and object request broker Future Directions Ongoing Concerns: e Ligbility e Quality guarantees e Contract persistence over versions