Scribble

Scribble is a simple text based language for describing interactions between multiple parties in the form of a Protocol.

"Scribbling is necessary for architects, either physical or computing, since all great ideas of architectural construction come from that unconscious moment, when you do not realise what it is, when there is no concrete shape, only a whisper which is not a whisper, an image which is not an image, somehow it starts to urge you in your mind, in so small a voice but how persistent it is, at that point you start scribbling" - Kohei Honda 2007

The Protocol notation is intended to provide an abstract description of the communication behaviour, with addtional optional layers being used to describe assertions and other governance related information.

In the world of programming languages, the measure of the simplicity of a language is based on its representation of a simple 'hello world' example. The Scribble Protocol representation of such an example would be:

			protocol HelloWorld {
			    participant You, World;
			    Hello from You to World;
			}
  		

The notation will be explained in more detail in this guide, but basically the protocol is named 'HelloWorld', and describes the communication behaviour between two participants (or parties). A single interaction has been defined, sending a message of type 'Hello' from participant 'You' to participant 'World'.

In the following chapter we will explore the main constructs of the protocol notation. Then we will explore a range of examples, before concluding with a brief overview of some more advanced constructs that are still under development.

This chapter presents some examples using the protocol notation.

protocol BuyerSeller {
    participant Buyer, Seller;
    
    Order from Buyer to Seller;
    
    choice from Seller to Buyer; {
        when Invoice {
        }
        when Rejected {
        }
	}
}
			

protocol CreditCheck {
    participant Client, CreditAgency;
    
    CheckCredit from Client to CreditAgency;
    
    choice from CreditAgency to Client {
        when CreditOk {
        }
        when NoCredit {
        }
    }
}
			

protocol BuyerSellerCreditCheck {
    participant Buyer, Seller, CreditAgency;
    
    Order from Buyer to Seller;
    
    CheckCredit from Seller to CreditAgency;
    
    choice from CreditAgency to Seller {
        when CreditOk {
        	Invoice from Seller to Buyer;
        }
        when NoCredit {
        	Rejected from Seller to Buyer;
        }
    }
}
			

This chapter describes constructs that are still work in progress.

This means that they may be included in the tool support for the notation, but may change in a future version. So any use of these constructs are not guaranteed to be supported in future versions of the tools.

parallel "{"
    ...
{ "}" and "{"
    ... }+
"}"
     		

parallel {
    CheckStock from Seller to Wholesaler;
    StockAvailability from Wholesaler to Seller;
} and {
    CreditCheck from Seller to CreditAgency;
    CreditReport from CreditAgency to Seller;
}
			

try "{"
    ...
{ (
"}" catch [ "@" <Participant> {"," <Participant>}* ] <Type> "{"
...
|
"}" interrupt [ "@" <Participant> {"," <Participant>} ] "{"
    ...
) }*
"}"
     		

try {
    repeat @ Seller {
        Quote from Seller to Buyer;
    }
} interrupt @ Buyer {
    AcceptQuote from Buyer to Seller
} interrupt @ Buyer {
    CancelQuote from Buyer to Seller
}
			

try {
    Enquiry from Buyer to Seller;
    repeat @ Seller {
        Quote from Seller to Buyer;
        choice @ Buyer {
            raise @ Buyer Quit;
        } or {
            ...;
        }
    }
} catch @ Buyer Quit {
    CancelQuote from Buyer to Seller
}
			

raise "@" <Participant> <Type>;
     		

try {
    Enquiry from Buyer to Seller;
    repeat @ Seller {
        Quote from Seller to Buyer;
        choice @ Buyer {
            raise @ Buyer Quit;
        }
    }
} catch @ Buyer Quit {
    CancelQuote from Buyer to Seller
}
			

unordered "{"
    ( <Activity1> ";" )+
"}"