Architectural Analysis Design Architectural Layers The Logical Architecture

Architectural Analysis & Design Architectural Layers The Logical Architecture is a large-scale organization of the software classes into packages (or namespaces), subsystems, and layers. Decisions about how these elements are to be deployed across physical computers in a networked environment are part of the Deployment Architecture. Classes in the system are grouped into layers. A layer is a coarse-grained grouping of classes, packages, or subsystems that has cohesive responsibility for a major aspect of the system. Layers are organized so that “higher” layers call upon services of “lower” layers, but not generally vice-versa.

Architectural Analysis & Design Architectural Layers • User Interface The user interface with the system may be through a graphical user interface or through web-based services. The user interface may consist of packages such as the swing package and the web package, where the swing package refers to the user generated classes that specialize the GUI framework • Application Logic and Domain Objects Software objects representing domain concepts. This layer may be divided into an Application layer containing facades for maintaining session state and controlling workflow to the Domain layer concpts. • Technical Services General purpose objects and subsystems that provide supporting technical services such as forming an interface with a database.

Architectural Analysis & Design Using layers helps address these problems: • Source code changes are rippling throughout the system – many parts of the system are highly coupled. • Application is intertwined with user interface, so it cannot be reused with a different interface or distributed to another processing node. • Potentially general technical services or business logic is intertwined with more application specific logic so it cannot be reused, distributed to another node, ore easily replaced with a different implementation. • There is high coupling across different areas of concern. It is difficult to divide the work along clear boundaries for different developers.

Architecture Analysis & Design GUI Windows, reports, speech, XML, HTML, JSP, Javascript Handles presentation layer requests, session state, workflow Handles application layer requests, implementation of domain rules& services Low-level business services such as currency conversion Higher-level technical services such as persistence & security Low-level technical services, utilities and frameworks such as data structures, threads, math, network I/O dependency UI (AKA Presentation, View) Application (AKA Workflow, Process, Mediation, Applic. Controller) Domain (AKA Bussiness, Application Logic) Business Infrastructure (AKA Low-level Business Services) Technical Services (AKA High-level Technical Services) Foundation (AKA Core Services, Base Services, Low-level Technical Services) Range of applicability More application specific

Architecture Analysis & Design Examples of UML notation for packages and layers Domain POS Inventory Tax Security Logging Vertical layers Technical Services Persistence Horizontal partitions Package or subsystem

Architecture Analysis & Design Guideline: Model-View Separation Principle 1. Do not connect or couple non-UI objects directly to UI objects. For example, do not let a Sale object have a reference to a JFrame window object. Windows are related to a particular application and platform, whereas the Domain objects may be reused in a new application or attached to a new interface. 2. Do not put application logic (such as tax collection) in the UI object methods. UI objects should only initialize UI elements, receive UI events (such as mouse clicks), and delegate requests for application logic to non-UI objects.

Architecture Analysis & Design UI Cashier System make. New. Sale() Swing … make. New. Sale( ) enter. Item(id, quantity) enter. Item(id, qt) Process. Sale Frame end. Sale( ) make. New. Sale() enter. Item(id, quant) description, total Domain end. Sale( ) …. . . Register make. New. Sale( ) enter. Item(id, quant) end. Sale( ) System Operations shown in SSD Implementation of System Operations

Designing a Persistence Framework This presentation illustrates the design of a persistence framework and the use of Design Patterns in constructing that framework. There are free, open-source persistence frameworks that you can use in your project. You do not have to create one of your own. In the Java domain, there is a widely used framework called Hibernate (www. hibernate. org).

Design of a Persistence Framework Domain Layer Persistence Framework Relational Database Persistence. Facade : University name = Cornell get(OID, class): Object put(OID, object) city = Ithaca University object Domain object will dematerialize when application goes out of scope Name City Harvard Cambridge Yale New Haven Michigan Ann Arbor Cornell Ithaca Store object in RDB put(OID, Retrievecornell. Obj) from RDB get(OID, University) University Table

Accessing Persistence Service with a Facade Pattern Intent Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use. Applicability • You want to layer your subsystem. Use Facade to define an entry point to each subsystem level. • Introduce a Facade to decouple subsystems from clients and other subsystems, thereby promoting subsystem independence and portability. • A Facade can produce a simple default view of the subsystem. Collaborations Clients communicate with the subsystem by sending requests to Façade, which forwards them to the appropriate subsystem object. Clients that use facade do not have to acess subsystem objects directly.

The Facade Pattern An Object Identifier Pattern We need a consistent way to relate objects to records in a database and be able to ensure that repeated materialization of a record does not result in duplicate objects. The Object Identifier Pattern proposes assigning an object identifier (OID) to each record and each object (or proxy of an object). An OID is an alphanumeric code that is unique to each object. Every table will have an OID as primary key

The Facade Pattern Mapping between persistent object and Database University Table OID name city uxh 345 Harvard Cambridge : University uxy 248 Yale New Haven name = Cornell uxm 117 Michigan Ann Arbor city = Ithaca uxc 123 Cornell Ithaca oid = uxc 123 primary key The OID may be contained in proxy object instead

The Facade Pattern : DBProduct. Adapter : Persistence. Facade pd = get(…) Persistence. Facade get. Instance(): Persistence Facade get(OID, class) put(OID, Object) //example use of the facade OID = new OID(“XYZ 123”); Product. Description pd = (Product. Description) Persistence. Facade. get. Insance(). get(oid, Product. Description. class);

The Database Broker What class should be responsible for the materialization and dematerialization of the objects from a persistent store? The Information Expert Pattern suggests that the persistent object class itself have this responsibility – It has some of the data (the data to be saved) required by the responsibility. This is termed Direct Mapping. Problems with the Direct Mapping approach include: • Strong coupling of the persistent object class to persistent storage knowledge – (violation of low coupling) • Complex responsibilities in a new and unrelated area to what the object was previously responsible for – (violation of high cohesion). Technical service concerns are mixing with application logic concerns.

The Database Broker Second option – use an indirect mapping approach. Create a Database. Mapper class that is responsible for the materialization and dematerialization of objects from the database. Each persistent object will have its own Mapper class.

The Facade Design Pattern with Brokers Persistence. Facade get. Instance( ): Persistence. Facade <<interface>> DBMapper class get(OID, class) : Object get(OID): Object put(OID, Object) put(OID, Object Product. Specification RDBMapper Product. Specification Flat. File. Mapper Manufacturer RDBMapper get(OID): Object put(OID, Object) put(OID, Object Each mapper gets and puts objects in its own unique way, depending on the kind of data store and format.

Facade Pattern with Brokers class Persistence. Facade { public Object get (OID oid, Class persistence. Class ) { DBMapper mapper = (DBMapper) mappers. get (persistencce. Class); //delegate return mapper. get(oid); } public put (OID oid, , Object obj) { Class persistence. Class = obj. get. Class( ); DBMapper mapper = (DBMapper) mappers. get (persistencce. Class); mapper. put(oid, obj); } }

Designing the Database. Mapper Classes The Template Method pattern should be used to: • Implement the invariant parts of an algorithm once and leave it to the subclasses to implement the behavior that can vary. • When common behavior among subclasses should be factored and localized in a common class to avoid code duplication. • To control subclass extensions. Abstract. Class Concrete. Class Template. Method( ) Primitive. Operation 1() Primitive. Operation 2( ) { …. . Primitive. Operation 1( ); ……. . Primitive. Operation 2(); …}

Template Pattern The Hollywood Principle: “Don’t call us, we’ll call you!” Example: The swing GUI framework //unvarying part of algorithm public void update { clear. Background( ); //call the hook method GUIComponent framework class update( ) Template method repaint( ) hook method repaint( ); } My. Button repaint( ) programmer’s class hook method overridden to supply class specific detail

Template Method Consider the POS Terminal Example <<interface>> DBMapper get(OID): Object put(OID): Object Abstract Persistence. Mapper +get(OID): Object {leaf} #get. Object. From. Storage( ): Object template method hook method {abstract}

Template Method Overriding the hook method DBMapper //template method public final Object get(OID oid) { obj = cached. Objects. get(oid); if (obj == null) { //hook method obj = get. Object. From. Storage(oid); cached. Object. put(oid, obj); } return obj; Abstract. Persistence. Mapper + get(OID): Object {concrete} # get. Object. From. Storage(OID): Object {abstract} } //hook method override protected Object get. Object. From. Storage(OID oid) { String key = oid. to. String( ); Product. Description RDBMapper db. Rec = SQL execution result of “Select* from PROD_DESC where key =“ +key Product. Description = new Product. Description(); pd. set. Price(db. Rec. get. Column(“PRICE”); etc # get. Object. From. Storage(OID): Object

Persistence Framework Next. Gen Persistence Product. Description RDBMapper Product. Description File. With. XMLMapper Sale. RDBMapper Product. Description In. Memory. Test. Data. Mapper Persistence. Facade class Abstract RDBMapper 1 <<interface>> DBMapper Abstract Persistence. Mapper

Template Method Implementation of Template Method in POSTerminal public class Persistence. Manager { public final Object get(OID oid) { //template method obj: = chached. Objects. get(OID oid); if (obj == null) { //hook method obj = get. Object. From. Storage(oid); cached. Object. put(oid, obj); } return obj; public class Product. Description. RDBMapper extends Persistence. Manager { protected Object get. Object. From. Storage(OID oid) { String key = oid. to. String( ); db. Rec = SQL execution result of “Select * from PROD_DESC where key = “ + key Product. Description pd = new Product. Description (); pd. set. OID(oid); pd. set. Price ( db. Rec. get. Column(“PRICE”) ); pd. set. Item. ID ( db. Rec. get. Column(“ITEM_ID”) ); pd. set. Description( db. Rec. get. Column(“DESC”) ); return pd; } ……. } } protected abstract Object get. Object. From. Storage(OID oid) ; }

Transactional States and the State Pattern Statechart for the Persistent. Object [new (not from DB)] New [from DB] save commit / insert Old. Clean rollback / reload commit / update Old. Dirty delete rollback / reload Deleted commit / delete Old. Delete

State Pattern Context/problem An object’s behavior is dependent upon its state, and its methods contain case logic reflecting conditional statedependent actions. Is there an alternative to conditional logic? Solution Create state classes for each state, implementing a common interface. Delegate state-dependent operations from the context object to the appropriate state object. Ensure the context object always points to the state object reflecting its current context.

State Pattern Collaborations (Example) TCPState TCPConnection Open( ) Close( ) Acknowledgement( ) state open( ) TCPEstablished TCPListen TCPClosed Open( ) Close( ) Acknowledgement( )

State Pattern Applying the State Pattern to the Persistence Framework PObject. State Persistent. Object oid: OID state: PObject. State commit( ) delete( ) 1 * rollback (Persistent. Object obj); save (Persistent. Object obj); Rollback( ) save( ) set. State(PObject. State) state commit( this ); commit (Persistent. Object obj); delete (Persistent. Object obj); Old. Dirty State Old. Clean State New State {//commit Persistence. Facade. get. Instance(). update(obj) obj. set. State(Old. Clean. State. get. Instance()} commit( …) delete(…) rollback(…) delete(…) save (…) commit( …)

Persistent Objects Domain Persistence Product. Description Persistent. Object oid: OID time. Stamp: Date. Time Sale commit( ) delete( ) rollback( ) save( ) Whenever a Domain object class extends a Technical Services class it should be done with hesitation and for a good reason. You will be mixing application logic and the technical concern of persistence.

Architectural Design Architectural Views • Logical Conceptual organization of the Architecture in terms of subsystems, packages, frameworks, classes, and interfaces. Summarizes the functionality of the major software elements. • Process Responsibilities, collaborations, and the allocation of responsibilty to processes and threads. • Deployment Physical deployment of processes and components to nodes and the network configuration between nodes. Overview of the data flows, persistent data schema, and the mapping • Data from objects to persistent data. Overview of the security schemes and points within the architecture • Security that security is applied. actual source code and executables. A summary of noteworthy • Implementation The deliverables. • Development • Use Case Summarizes information developers need to know about the setup of the development environment – directory structure, version control, etc. Summary of the most architecturally significant use cases and their nonfunctional requirements. Summary of those use cases that illustrate significant architectural coverage or exercise many arch. elements.