Documented usage

README.md

@@ -14,6 +14,62 @@ Install with the following command:
 composer require cloudobjects/sdk
 ``` 
 
+## Usage
+
+The primary purpose of the SDK is the retrieval of object descriptions from the CloudObjects Core Object API. To do so, you create an instance of the `CloudObjects\SDK\ObjectRetriever` class. You can use this class directy, but you can also use the static facade (`CloudObjects\SDK\ObjectRetrieverFacade`) or the global function `cloudobjects_get_object()`, depending on the architecture of your PHP application and your preferred coding style. You can use the high-level `CloudObjects\SDK\CloudObject` interface or the lower-level `ML\JsonLD\Node` interface to work with the parsed JSON-LD representation of the object.
+
+### Using the ObjectRetriever directly
+
+```php
+use CloudObjects\SDK\ObjectRetriever;
+use ML\IRI\IRI;
+
+$retriever = new ObjectRetriever;
+$object = $retriever->getCloudObject(new IRI('coid://cloudobjects.io'));
+echo $object->getLabel();
+```
+
+### Using the static facade
+
+```php
+use CloudObjects\SDK\ObjectRetriever;
+use CloudObjects\SDK\ObjectRetrieverFacade;
+use ML\IRI\IRI;
+
+ObjectRetrieverFacade::setObjectRetriever(new ObjectRetriever());
+
+$object = ObjectRetrieverFacade::getCloudObject(new IRI('coid://cloudobjects.io'));
+echo $object->getLabel();
+```
+
+### Using the global function
+
+The global function uses the static facade, so the facade must be initialized first.
+
+```php
+use CloudObjects\SDK\ObjectRetriever;
+use CloudObjects\SDK\ObjectRetrieverFacade;
+
+ObjectRetrieverFacade::setObjectRetriever(new ObjectRetriever());
+
+$object = cloudobjects_get_object('coid://cloudobjects.io');
+echo $object->getLabel();
+```
+
+### Working with the `CloudObject` interface
+
+```php
+$object = $retriever->getCloudObject(new IRI('coid://cloudobjects.io'));
+echo $object->getString('http://www.w3.org/2000/01/rdf-schema#comment');
+```
+
+### Working with the `Node` interface
+
+```php
+$node = $retriever->getObjectNode(new IRI('coid://cloudobjects.io'));
+echo $node->getProperty('http://www.w3.org/2000/01/rdf-schema#comment')->getValue();
+```
+
 ## License
 
 The PHP SDK is licensed under Mozilla Public License (see LICENSE file).