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Principles of Object-Oriented Software Development
Software Architecture
Software Architecture
Introduction
Elements of architecture Case study -- multimedia feature detection Crossing boundaries Architectural patterns and styles Cross-platform development
Summary Q/A Literature
Software architecture• architecture -- components and boundaries
• case study -- a framework for multimedia feature detection
• native objects -- the language boundary
• embedded logic -- the paradigm boundary
• architectural styles -- distributed object technology
• cross-platform development -- Unix versus Windows
Additional keywords and phrases:components, information architecture, multimedia information retrieval, feature detection, portability
Elements of Architecture
• processing elements -- transformation on data
• data elements -- contain information
• connections -- glue that holds elements together
[Wolf]
Models and Views
• logical -- functional requirements
• process -- performance, availability, distribution
• physical -- scalability, configuration
• development -- organization of software modules
• scenarios -- instances of use cases
Definitions
http://www.sei.cmu.edu/architecture/definitions.html
[Kruchten95]
The software architecture of aprogram or computing system is thestructure of the system, whichcomprises software components, theexternally visible properties of thosecomponents, and theirinterrelationships.
Bass et al.
Technological infrastructure
• client-platform -- hardware, OS
• presentation services -- windows, multimedia
• application software -- code, business logic
• network -- communication support
• middleware -- distribution, (object) brokers
• server platform -- hardware, OS
• database -- data management system
[CS2001]
Distributed Object Patterns
Framework (class hierarchies)
Applications (wrappers)
System (horizontal, vertical, metadata)
Enterprise (reference models, infrastructure, policies)
Intra/Internet (standards)
[CorbaPatterns]
Case study
multimedia feature detection
The extended ACOI architecture
The ACOI frameworkdetector world; finds the name of the world
detector people; checks name, eliminates institutes
detector company; looks if there are at least two persons
atom str name; community: world people company; world: name; people: person*; person: name; A sample grammar
int personDetector(tree *pt, list *tks ){ ... q = query_query("kit=pl src=check.pl"); while (t = next_token(tks)) { sprintf(buf,"person(\%s)",t); query_eval(q,buf); if (query_result(q,0)) // put name(person) on tokenstream putAtom(tks,"name",t); } ... }
A person detector
V0 := newoid(); V1 := newoid(); community_world.insert(oid(V0),oid(V1)); world_name.insert(oid(V1),"casa"); community_people.insert(oid(V0),oid(V1)); V2 := newoid(); people_person.insert(oid(V1),oid(V2)); person_name.insert(oid(V2),"alice"); people_person.insert(oid(V1),oid(V2)); person_name.insert(oid(V2),"sebastiaan"); ...
Database updates
The anatomy of a MIDI feature detector
MIDI features
detector song; to get the filename
detector lyrics; extracts lyrics
detector melody; extracts melody
atom str name; atom str text; atom str note; song: file lyrics melody; file: name; lyrics: text*; melody: note*;
A simple feature grammar for MIDI files
event('kortjakje',2,time=384, note_on:[chan=2,pitch=72,vol=111]). event('kortjakje',2,time=768, note_off:[chan=2,pitch=72,vol=100]).
Prolog representation
Processing MIDI file
int melodyDetector(tree *pt, list *tks ){ char buf[1024]; char* _result; void* q = _query; int idq = 0; idq = query_eval(q,"X:melody(X)"); while ((_result = query_result(q,idq)) ) { printf("note: \%s",_result); putAtom(tks,"note",_result); } return SUCCESS; }
The melody detector
Queries -- the user interface
Keyboard interface
User Query Processing
Crossing boundaries
Subsections:
Embedded logic -- crossing the paradigm boundary Native objects -- crossing the language boundary Combining Java and C++
Embedded Logic -- crossing the paradigm boundary
<query kit=pl src=local.pl cmd=X:email_address(X)> <param format=" \%s"> <param result=""> <param display="<h4>The query</h4>"> <param header="<h4>The adresses</h4> <ul>"> <param footer="</ul>"> email_address(E) :- person(X), property(X,name:N), property(X,familyname:F), email(X,E), cout(['<li>', N,' ',F,' has email adress ']), cout([ '<a href=mailto:', E, '>', E, '</a>',nl]). </query>
query pl = new query("kit=pl src=remote.pl"); logic.java
pl.eval("X:assistant(X)"); String res = null; while ( (res = pl.result()) != null ) { System.out.println("<li> " + res); }
Distributed knowledge servers
remote.pl
:- source('http://www.cs.vu.nl/~eliens/db/se/people.pl'). :- source('http://www.cs.vu.nl/~eliens/db/se/institute.pl'). :- source('http://www.cs.vu.nl/~eliens/db/se/property.pl'). :- source('http://www.cs.vu.nl/~eliens/db/se/query.pl').
interface query { query.idl
void source(in string file); long eval(in string cmd); string result(in long id); oneway void halt(); };
Native objects
crossing the language boundary
Objects in Prolog
• representation -- object(Handler,Class,ID,REF,Ancestors)
• object definition -- class_method(This,...)
• object invocation -- self(This):method(...)
• state variables representation -- value(ID,Key,Value)
• state variable access -- var(Key) = Value, Var = value(key)
• native binding - native(Handler,Method,Result)
• low overhead, especially when not needed
• natural syntax for object clause definitions
• support for native objects
midi(This):midi, create midi object
Self = self(This), Self:open('a.mid'), Self:header(0,1,480), Self:track(start), Self:melody([48,50,51,53,55]), // c d es f g, minor indeed Self:track(end), end track
native methods midi_read(This,F) :- native(_,This,read(F),_). midi_analyse(This,I,O) :- native(_,This,analyse(I,O),_). midi_open(This,F) :- native(_,This,open(F),_). midi_header(This,M) :- native(_,This,header(M,0,480),_). midi_track(This,X) :- native(_,This,track(X),_). midi_tempo(This,X) :- native(_,This,tempo(X),_). midi_event(This,D,C,M,T,V) :- native(_,This,event(D,C,M,T,V),_).
midi :- use(library(midi:[midi,lily,music,process])). :- declare(midi:object,class(midi),[handler]). midi_midi(This) :- constructor
midi(This):handler(H), // gets Handler from class declare(H,new(midi(This)),[],[],_).
midi_note(This,D,C,T,V) :- Self = midi(This), cast to midi
Self:event(D,C,note_on,T,V), Self:event(D,C,note_off,T,V). midi_melody(This,L) :- self(This):melody(480,1,L,64). midi_melody(_This,_,_,[],_). midi_melody(This,D,C,[X|R],V) :- Self = self(This), Self:note(D,C,X,V), midi_melody(This,D,C,R,V). direct invocation
C++ bindings
int kit_object::operator()() { kit_object event* e = _event; vm<kit> self(e); smart pointer string method = e->_method(); if (method == "kit") { constructor kit* q = new kit(e->arg(1)); _register(q); result( reference((void*)q) ); } else if (method == "eval") { long res = self->eval(e->arg(1)); result( itoa(res) ); } else if (method == "result") { char* res = self->result( atoi(e->arg(1)) ); result(res); } else { // dispatch up in the hierarchy return handler_object::operator()(); } return 0; }
template <class T>class vm { smart pointer class public: vm(event* e) { int p = 0; char* id = e->option("ref"); if (id) { p = atoi(id); } _self = (T*) p; } virtual inline T* operator->() { return _self; } private: T* _self; };
Combining Java and C++
package hush.dv.api; class obscure { obscure
public int _self; peer object pointer
... };
package hush.dv.api;
public class kit extends handler { kit public kit() { _self = init(); } protected kit(int x) { } private native int init(); public native void source(String cmd); public native void eval(String cmd); public String result() { String _result = getresult(); if (_result.equals("-")) return null; else return _result; } private native String getresult(); public native void bind(String cmd, handler h); ... };
kit.c #include <hush/hush.h> #include <hush/java.h> #include <native/hush_dv_api_kit.h> #define method(X) Java_hush_dv_api_kit_##X JNIEXPORT jint JNICALL method(init)(JNIEnv *env, jobject obj) { jint result = (jint) kit::_default; // (jint) new kit(); if (!result) { kit* x = new kit("tk"); session::_default->_register(x); result = (jint) x; } return result; }
JNIEXPORT jstring JNICALL method(getresult)(JNIEnv *env, jobject obj) { java_vm vm(env,obj); char *s = vm->result(); if (s) return vm.string(s); else return vm.string("-"); }
JNIEXPORT void JNICALL method(bind)(JNIEnv *env, jobject obj, jstring s, jobject o) { java_vm vm(env,obj); java_vm* vmp = new java_vm(env,o,"Handler"); const char *str = vm.get(s); handler* h = new handler(); session::_default->_register(h); h->_vmp = vmp; h->_register(vmp); vm->bind(str,h); vm.release(s, str); }
handler::dispatch event* handler::dispatch(event* e) { _event = e; if (_vmp) { return ((vm*)_vmp)->dispatch(e); } else { int result = this->operator()(); if (result != OK) return 0; else return _event; } }
#include <hush/vm.h> #include template< class T > class java_vm : public vm< T > { java_vm public: java_vm(JNIEnv* env_, jobject obj_) { _env = env_; _obj = obj_; _self = self(); } ...event* dispatch(event* e) { java dispatch call("dispatch",(int)e); return e; }
T* operator->() { return _self; } T* self() { jfieldID fid = fieldID("_self","I"); return (T*) _env->GetIntField( _obj, fid); } void call(const char* md, int i) { // void (*)(int) jmethodID mid = methodID(md,"(I)V"); _env->CallVoidMethod(_obj, mid, i); } private: JNIEnv* _env; jobject _obj; T* _self; };
Architectural patterns and styles
Subsections:
From technology to style Case study -- perspectives in visualization
From technology to style
• the distributed objects style
• the (dynamically) downloadable code style
• the mobile objects style
distributed downloadable mobile objects code objects
Component object object/class agent Connector ORB various methods Creation server client any Location server client any Client fixed extensible extensible Server extensible fixed extensible
Feature classification
Case study -- perspectives in visualization
Exchanging perspectives
Guidelines for selecting a style
Rules of thumb -- selecting an architectural style
Dedicated hardware or legacy code distributed objectsStrategic or secret code distributed objectsMany users downloadable codePeriodic updates downloadable codeCommunication and negotiation mobile objects
Cross-platform development
Cross-platform development
• open toolkits and standards -- OMG CORBA
Unix vs NT
Research/GNU
AT&T U/WIN -- Posix for 95/NT Cygnus -- GNU-win32
Commercial
NuTCracker/MKS -- porting Unix applications to Windows Wind/U, Mainwin -- porting Windows applications to Unix Tributary -- developing Unix applications from Windows IDE
• deploying platform independent toolkits
• porting applications from Unix to Windows
• porting applications from Windows to Unix
Summary
Elements of architecture
• processing elements -- transformation on data
• data elements -- contain information
• connections -- glue that holds elements together
1
Case study -- multimediafeature detection
• feature grammar -- structure
• embedded logic -- rules for recognition
• architecture -- multimedia information system
2
Crossing boundaries
• embedded logic -- crossing the paradigm boundary
• native objects -- crossing the language boundary
• combining Java and C++
3
Architectural patterns and styles
• technology matrix -- from technology to style
• case study -- visualization perspectives
4
Cross-platform development
• from Unix to Windows -- AT&T U/Win, Cygnus GNU-win32
• from Windows to Unix -- Wind/U, Mainwin
5
Questions1. What are the elements of a software architecture? What role plays a software architecture description in development? 2. Give a definition of software architecture? Can you think of alternative definitions? 3. What kind of patterns can you think of for distributed object architectures? 4. Give an example of a complex software architecture. Can you relate the description of the architecture to the definition given earlier? 5. Discuss the possible motivations for deploying embedded logic. 6. How would you extend a given imperative or declarative language with objects? 7. Discuss the Java Native Interface. Does it provide a solution for the problem posed in the previous question? Explain. 8. What determines the choice for an architectural style? Give an example!
Further reading
An excellent book on software architectures is [Practice]. You may also want to visit the SEI architecture site at http://www.sei.cmu.edu/architecture, which provides definitions, and a wealth of other information. As a discussion of the software engineering implications of CORBA, you may want to read [CorbaPatterns]. If you are interested in multimedia information systems, read [MM]. For more information on ACOI, visit the ACOI website on http://www.cwi.nl/~acoi .
