Study Group 17 ASN.1 The importance of colour John Larmouth ISO ASN.1 Rapporteur Note, for best viewing, this presentation needs the Dom Casual and Brush Script fonts. Study Group 17 ASN.1

Black and White is bad! n The Black and White Minstrel Show n Black and White TVs n The latest Nokia phone!

Study Group 17 ASN.1 Colour is good! n The deep blue of the sky n Sunlight shining on the ground n Leaves in the Autumn n Printers and photocopiers n Colouring illuminates!

Study Group 17 ASN.1 What is colouring? n Colouring is the application of detail to a specification n For some, not necessary n For others, important

Study Group 17 ASN.1 What is SDL, UML, UBL about? n They are about easy specification of distributed processes n The are about the semantics (and sequences) of the messages that are exchanged in a protocol

Study Group 17 ASN.1 What is not necessary? (Or is it?) n Notation used to define the syntax of messages (ASN.1, XSD specification, table notation) n Detailed syntax specification n Control of encodings n Extensibility identification n Sub-typing (constraints)

Study Group 17 ASN.1 Business processes matter! But bits on the line matter as well! n How much can be automated? n How much help is needed? n How to provide that help?

Study Group 17 ASN.1 The ASN.1 colouring concept n Used in XCN n Used in ECN n A separate specification at a different level of detail, but closely linked to the higher-level specification

Study Group 17 ASN.1 Example 1 – XCN colouring ASN.1: TraceCollection ::= SEQUENCE { version UTF8String DEFAULT "1.0”, collectionBeginTimeDateTime, vendorUTF8String OPTIONAL, senderSender OPTIONAL, callsSEQUENCE SIZE (1..MAX) OF call Call } Colouring for XML: ATTRIBUTE version, collectionBeginTime IN TraceCollection

Study Group 17 ASN.1 Example 2 – ECN colouring ASN.1: Sequence2 ::= SEQUENCE{ component1BOOLEAN OPTIONAL, component2INTEGER, component3VisibleStringOPTIONAL } Colouring for ECN: RENAME #OPTIONAL AS #Sequence2-optional IN #Sequence2 -- #Sequence2-optional is a special encoding for optionality -- #Sequence2-optional is a special encoding for optionality -- Other optionals encode in the normal way. -- Other optionals encode in the normal way.

Study Group 17 ASN.1 What is colouring? (1) Colouring is the application of detail that is irrelevant in the development of the base specification. Colouring is the application of detail that is irrelevant in the development of the base specification.

Study Group 17 ASN.1 What is colouring? (2) But detail that is essential for the efficient generation of lower-level specifications, down to encodings But detail that is essential for the efficient generation of lower-level specifications, down to encodings

Study Group 17 ASN.1 What can colouring be used for? n Ranges and subtypes (minimum set of abstract values) n Extensibility needs n Processing Instructions (low level control)

Study Group 17 ASN.1 Different targets for colouring in ASN.1 n BER needs tags n PER needs clear extensibility requirements and sub-typing n XML needs attribute and TEXT and UNTAGGED etc n ECN needs identification of specially-encoded constructors

Study Group 17 ASN.1 Requirements Analysis Top-level design – SDL, UML, UBL (only essential info?) ECN PER BER XER Possible implementation routes XSD ASN.1 Tables BNF Possible implementation routes Detail is needed at each level. How to add it without confusing the simple design? How to add it without confusing the simple design? Add detail with colouring.

Study Group 17 ASN.1 The W-5 n Who will provide the details? (Relevant experts) n Why do we want details as well as top- level design? (The details matter) n Where do we record the details? (Embedded, Colouring, Boxes) n What details need to be included? (Anything necessary for efficient lower-layer mappings) n Which implementation mappings? (Detail for several notations, several encodings)

Study Group 17 ASN.1 But three is good! n The three ages of man n The three fates n The three faces of Buddha n The three fundamental forces

Study Group 17 ASN.1 The three experts n Domain (business) experts n Notation experts ASK FOR MORE DETAIL on sub-typing, extensibility n Encoding experts ASK FOR MORE DETAIL on bandwidth needs, readability, encoding choices This all needs adding to the base specification - perhaps the colouring metaphor will help

Study Group 17 ASN.1 Colouring n An architectural concept n Has proved useful in ASN.1 n Part of information hiding n Keeps top-level independent of lower layer implementation n Ensures lower layer details needed for efficient operation can be easily provided Colour is good!