oop - Modular design and intermodule references -

i'm not sure title match question want put on table.

i'm planning create web mvc framework graduation dissertation , in previous conversation advisor trying define achivements, convinced me should choose modular design in project.

i had things developed , stopped while analyze how modular , couldn't because don't know real meaning of "modular".

some things not cleary me, example, referencing module blows modularity of system?

let's have database access module , optionaly can use cache module storing results of complex queries. can see, @ least have naming dependency cache module.

in conception of "modular design", can distribute each component separately , make interact others developed other people. in case showed, if wants use database access module, have take cache well, if not use it, referencing/naming purposes.

and so, wondering if modular design yet.

i came alternative creating each component singly, without don't knowing existance of other components not absolutely required functioning. extend functionalities, create structure based on decorators , adapters.

to clarify things little bit, here example (in php):

before

interface cache {     public function isvalid();     public function setvalue();     public function getvalue(); }  interface cachemanager {     public function get($name);     public function put($name, $value); }  // concrete implementations...  interface dbaccessinterface {     public docomplexoperation(); }  class dbaccess implements dbaccessinterface {     private $cachemanager;      public function __construct(..., cachemanager $cachemanager = null) {         // ...         $this->cachemanager = $cachemanager;     }      public function docomplexoperation() {         if ($this->cachemanager !== null) {             // return cache if valid         }          // complex operation     } } 

after

interface cache {     public function isvalid();     public function setvalue();     public function getvalue(); }  interface cachemanager {     public function get($name);     public function put($name, $value); }  // concrete implementations...  interface dbaccessinterface {     public function docomplexoperation(); }  class dbaccess implements dbaccessinterface {     public function __construct(...) {         // ...     }      public function docomplexquery() {         // complex operation     } }  // , integration module  class cacheddbacess implements dbaccessinterface {     private $dbaccess;     private $cachemanager;      public function __construct(dbaccessinterface $dbaccess, cachemanager $cachemanager) {         $this->dbaccess = $dbaccess;         $this->cachemanager = $cachemanager;     }      public function docomplexoperation() {         $cache = $this->cachemanager->get("foo")         if($cache->isvalid()) {             return $cache->getvalue();         }         // complex operation...     } } 

now question is: best solution? should modules not have requirement work together, can more efficient doing so?

anyone in different way?

i have more further questions involving this, don't know if acceptable question stackoverflow.

p.s.: english not first language, maybe parts can little bit confuse

some resources (not theoretical):

• nuclex plugin architecture

• python plugin application

• c++ plugin architecture (use noscript on side, have weird login policies)

• other threads (design pattern plugins in php)

• django middleware concept