Software Architecture Patterns (2)

what is architecture? (recap) o an overall blueprint/model describing the structures and properties of a "system" o designed mechanisms (causal chains & loops) which lead to - o emergent (intended) behaviour (but always some unintended behaviour as well) o"mapping" the boundaries (questions about the level of "closure")

software architecture… - Captures the gross structure of a system - How it is composed of interacting parts - How the interactions take place - Key properties of the parts - Provides a way of analysing systems at a high level of abstraction ! - Illuminates top-level design decisions

software architecture patterns Architectural pattern are software patterns that offer well-established solutions to architectural problems in software engineering. It gives description of the elements and relation type together with a set of constraints on how they may be used. An architectural pattern expresses a fundamental structural organization schema for a software system, which consists of subsystems, their responsibilities and interrelations. In comparison to design patterns, architectural patterns are larger in scale. Wikipedia

typical architectural patterns (styles) File Transfer Shared Database - How can I integrate multiple applications so that they work together and can exchange information? integration styles for (enterprise) messaging Remote Procedure Messaging

pipes and filters The Pipes and Filters architectural pattern [style] provides a structure for systems that process a stream of data. Each processing step is encapsulated in a filter component. Data is passed through pipes between adjacent filters. Recombining filters allows you to build families of related systems. [POSA p53]

example: traditional ‘nix pipes & filters e.g. using sed and awk

example: Apache Cacoon’s pipes & xslt filters

tiered architecture (layering) 2 - tier architecture (traditional client-server) A two-way interaction in a client/server environment, in which the user interface is stored in the client and the data are stored in the server. The application logic can be in either the client or the server.

3 tier architecture

model-view-controller (1) The MVC paradigm is a way of breaking an application, or even just a piece of an application's interface, into three parts: the model, the view, and the controller. MVC was originally developed to map the traditional input, processing, output roles into the GUI realm: Input  Processing  Output Controller  Model  View

model-view-controller (2) The pattern isolates business logic from input and presentation, permitting independent development, testing and maintenance of each.

mvc Model It is the domain-specific representation of the data on which the application operates. Domain logic adds meaning to raw data (for example, calculating whether today is the user's birthday, or the totals, taxes, and shipping charges for shopping cart items). When a model changes its state, it notifies its associated views so they can refresh. Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention the data access layer because it is understood to be underneath or encapsulated by the model. Models are not data access objects although in very simple apps, with little domain logic, there is no real distinction to be made. Also, the ActiveRecord is an accepted design pattern which merges domain logic and data access code - a model which knows how to persist itself.

mvc View Renders the model into a form suitable for interaction, typically a user interface element. Multiple views can exist for a single model for different purposes. mvc Controller Receives input and initiates a response by making calls on model objects. An MVC application may be a collection of model/view/controller triplets, each responsible for a different UI element.

PHP MVC Frameworks lots and lots… codeigniter, cake, kohana, jelix, limonade, mojavi, zend, zoop, symfony etc. etc. see:

mvc fat v. thin controllers ruby on rails ‘fat’ model, ‘thin’ controller approach watch:

rails Mvc : model ActiveRecord : –Maintains the relationship between Object and Database and handles validation, association, transactions, and more. –This subsystem is implemented in ActiveRecord library which provides an interface and binding between the tables in a relational database and the Ruby program code that manipulates database records. Ruby method names are automatically generated from the field names of database tables, and so on.

ActionView : –A presentation of data in a particular format, triggered by a controller's decision to present the data. They are script based templating systems like JSP, ASP, PHP and very easy to integrate with AJAX technology. –This subsystem is implemented in ActionView library which is an Embedded Ruby (ERb) based system for defining presentation templates for data presentation. Every Web connection to a Rails application results in the displaying of a view. rails mVc : view

rails mvC : controller ActionController : –The facility within the application that directs traffic, on the one hand querying the models for specific data, and on the other hand organizing that data (searching, sorting, massaging it) into a form that fits the needs of a given view. –This subsystem is implemented in ActionController which is a data broker sitting between ActiveRecord (the database interface) and ActionView (the presentation engine).