If you come to my desk, you will see several things you might not expect. You will find four or five things I created with Lego Blocks. I use those during meetings to bring that metaphor into the conversation.
Lego Blocks are valuable BECAUSE they have a Uniform Standard Interface that makes them Reusable, Intrinsically Interoperable and Composable.
In this six minute video you will see all the elements of SOA in play from a metaphorical level.
In this video you will see a desk that contains all the Lego Blocks separated by attributes, just like an Enterprise Service Registry will contain all the metadata of available Services.
Each Block Type is representative of an agnostic Service. Those blocks that have just One Pin and One Socket are just Like Atomic Services. The base plates are just like and Enterprise Service Bus that allows ANY of the other Blocks/Services to plug in and Interoperate.
The larger Blocks with multiple pins and sockets are like Composite services with multiple entry points. See how many other SOA service type are represented.
Just like a Lego Builder searches his Desk drawers for the Blocks he needs, a solution architect will search his service inventory to assemble his solutions.
So ah, what you need to do is create your services with Uniform Standadized Service contracts and you can build solutions as easy as building a Lego Creation.