Implementation Architecture Lecture 20- 22

Implementation View (1) Focuses on “how the system is built” Which technological elements are needed to implement the system: Software packages (req. Development tools), Libraries (implementing behavior e.g. “Cout”), Frameworks (Generic functionality e.g. “JUnit”), Classes , ... Addresses non-runtime quality attributes: Configurability (e.g. Platform), Testability (e.g. Mapping of FRs), Reusability

Implementation View (2) Again, comprised of components and connectors Here, components and connectors reflect “Software entities and their relationships at the level of source and binary code” Typically a number of implementation models can be developed Each model focuses on the concurrent subsystems/processes from the execution view.

A view focussing on… Build-time structure: Detailed activity As, implementation architecture focuses on the “built-time” structure of the system. Build-time structure: Implementation modules Off-the-shelf technology Build-time configuration Detailed activity Call sequences i.e. Sequence Diagram

Components in implementation architecture (1) Two types of components: Application components And infrastructure components

Components in implementation architecture (2) Application components: “Are responsible for implementing domain-level responsibilities” These are responsibilities found in a detailed conceptual architecture Application components might be realized as: Source packages, And files

Components in implementation architecture (3) Infrastructure components: “Are needed to make the system run but are not related to the application functionality” e.g. LAN Connection Handler in Distributive system is a typical infrastructure component (Just use to connect local systems, so they can communicate when they require)

Components in implementation architecture (4) Often an infrastructure component acts as a "container" for application components A container component provides an execution environment for the contained components (application components) Typically, the container executes within a process and creates threads for application components e.g. a Web application server which runs multiple applications from multiple users, each of them in their own threads.

Component stereotypes in implementation view Infrastructure component Containers Application components

Connectors in implementation architecture (1) In implementation architecture connectors represent: “a "uses" relation” The arrow depicts the direction of this relation The nature of communication is depicted through the connector styles

Connectors in implementation architecture (2) API call: A component calls a method in another component (possibly only if both components are in the same process) Callback: The caller passes a reference of an object to the “callee” (called component). The “callee” invokes a method (desired computation) on that object later and return the results to caller.

Connectors in implementation architecture (3) Network protocol: Needed when implementation components reside in different physical layer. Components need to agree on a common protocol or use a standardized protocol OS signals: Communication between processes running on the same machine

Connectors in implementation architecture (4)

Connectors in implementation architecture (5) In some cases, we represent ports as: “endpoints of connectors between components” Ports are used to identify a particular interface For example: A component might be quite complex but it provides a simple interface for communication e.g. the standard Java library provides an API (Application Programming Interface).

Simple “two-tier” web app Infrastructure component Apache Apache module API Ports HTTP mod_php Containers Application components MySQL Data Model/s

Conceptual v/s implementation Architecture Implementation Architecture Domain-level responsibilities Implementation module Component Flow of information “Uses” relationship Connector

Implementation architecture design Find application components Find infrastructure components Interface design Behavior design and verification

Application components (1) 1-to-1 mapping: of conceptual components onto application components is typically not possible. Some conceptual components will become infrastructure components. e.g. persistent storage (databases) are typically infrastructure components Some conceptual components are spread over a number of application components Conceptual components have complex responsibilities e.g. Application layer (Request acceptor , Request Handler e.t.c)

Application components (2) A number of conceptual components can be mapped onto a single application component E.g. small number and simple responsibilities MPS system is such an example: All UI components map onto one application component (i.e. HTML UI)

Infrastructure components Off-the-shelf components (e.g. Third party services) Frameworks (e.g. application framework) Servers (web, application, database, file) Generic clients (browser) In MPS system two infrastructure components: Browser, Application server

Interface design For all application and infrastructure components we need to define “interfaces” (ports) Helps in clarifying the “way to connect” the components Some interfaces are also standardized e.g. HTTP Connectivity, SQL Connectivity UI: Combination of HTML/HTTP It is standardized!

Behavior design Now we need to go into details Use-case maps are not enough anymore We need to investigate behavior at the operation level Thus, we need a sequence diagram

MPS: Implementation Architecture

Non-runtime quality attributes Since implementation view addresses build structure It is the right place to consider non-runtime quality attributes, e.g. Maintainability, Extensibility, Reusability, ... We can use a mechanism similar to use-case maps Impact-maps: “try to investigate what parts of the system need to change if "something" happens”

Impact-maps Map 1: new external system Map 2: new application interface to external system needs to be changed Map 2: new application application component needs to be changed Map 3: new UI UI component needs to be changed

Implementation arch. summary What you need to submit at end of Implementation Architecture: Detailed implementation architecture with app, infrastructure and interfaces Sequence diagram of application interfaces

Prototype To show that the architectural solution is feasible, we implement prototypes: For each identified application component we provide implementation Deploy it within the infrastructure components Test it and check: Correctness, Functionality, Quality-attributes

Dimensions of prototypes (1) Horizontal Prototype: A common term for a “user interface” prototype is the horizontal prototype. It provides a broad view of an entire system or subsystem, focusing on user interaction more than low-level system functionality, such as database access. Horizontal prototypes are useful for: Confirmation of user interface requirements and system scope Develop preliminary estimates of development time, cost and effort.

Dimensions of prototypes (2) Vertical Prototype: “A vertical prototype is a more complete elaboration of a single subsystem or function” It is useful for obtaining detailed requirements for a given function, with the following benefits: Refinement database design Clarifies complex requirements by drilling down to actual system functionality

Technical prototypes (1) Throwaway or Rapid Prototyping refers to: “creation of a model that will eventually be discarded rather than becoming part of the final delivered software” A simple working model of the system is constructed to visually show the users what their requirements may look like when they are implemented into a finished system. Also called close-ended prototyping.

Technical prototypes (2) A “throw-away” The prototype code is not part of the delivered system No concern for irrelevant quality attributes (performance, robustness) Purely to gain knowledge (or confidence): Test a new version of a commercial component Verify that a set of components work together Examine performance trade-offs Verify that a proposed architecture is sound

Technical prototypes (3) Evolutionary Prototyping: “the main goal is to build a very healthy prototype in a planned manner and constantly refine it.” The reason for this is that the Evolutionary prototype, when built, forms the heart of the new system, and the improvements and further requirements will be built. When developing a system using Evolutionary Prototyping, the system is continually refined and rebuilt.

Technical prototypes (4) This technique allows the development team to: Add features, Or make changes Evolutionary Prototypes have an advantage that they are functional systems. They may be used on temporary basis until the final system is delivered.