Using Subobject

$subject = new DIWikiPage( 'Foo', NS_MAIN );

$subobject = new Subobject( $subject->getTitle() );
$subobject->setEmptyContainerForId( 'SomeSubobject' );

$dataValue = DataValueFactory::getInstance()->newDataValueByText(
    'SomeProperty,
    'SomeValue'
);

$subobject->addDataValue(
    $dataValue
);

// Create and store SemanticData object and add the subobject
$semanticData = new SemanticData( $subject );

$semanticData->addPropertyObjectValue(
    $subobject->getProperty(),
    $subobject->getContainer()
);

ApplicationFactory::getInstance()->getStore()->updateData(
    $semanticData
);

Using DIContainer

$subject = new DIWikiPage( 'Foo', NS_MAIN );

// Internal subobject reference
$subobjectName = 'SomeSubobject';

$containerSubject = new DIWikiPage(
    $subject->getDBkey(),
    $subject->getNamespace(),
    $subject->getInterwiki(),
    $subobjectName
);

// Create container to host property values assignments
// for the particular subobjectName
$containerSemanticData = new ContainerSemanticData( $containerSubject );

$dataValue = DataValueFactory::getInstance()->newDataValueByText(
    'SomeProperty,
    'SomeValue'
);

$containerSemanticData->addDataValue(
    $dataValue
);

// Create and store SemanticData object and add the subobject
$semanticData = new SemanticData( $subject );

$semanticData->addPropertyObjectValue(
    new DIProperty( '_SOBJ' ),
    new DIContainer( $containerSemanticData )
);

ApplicationFactory::getInstance()->getStore()->updateData(
    $semanticData
);