SMIng%20Requirements

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SMIng Requirements

• Andrea Westerinen

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What Is the End Game?

• As part of requirements, need to understand the
  goals
• Several options
• Merge SMI and SPPI (only)
• Merge SMI/SPPI and add new capabilities
• Be the ASCII representation for IETF information
  models, and allow mapping to MIBs, PIBs and other
  data modeling languages

Today
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What Is an Information Model?

• Models key concepts
• Object-oriented approach recommended
• Encapsulation/abstraction, classes and instances,
  attributes/properties, behavior, actions/methods,
  notifications, inheritance, relationships/associat
  ions
• Protocol independent
• Can be mapped to a variety of implementations and
  data representations (sometimes from one
  construct to many)

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What Is a Data Model?

• Implementation specific
• Data representation specific
• May include protocol specific optimizations
• Ideally derived from an information model,
  typically not true today

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IETF Examples of Info/Data Models

• DiffServ WG
• Informal Model English text
• Information Model would formalize this English
  text
• MIB and PIB are data models that should be
  aligned with the info model
• Process not without its pain
• Forces design before coding
• Formal info model should ease this pain (Less
  ambiguous than English)
• Can iterate the models as they are coded

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Requirements for SMIng

• Naming of classes
• Instances named relative to their protocol/data
  model (MIBs, PIBs, )
• Definition of basic data types (including
  pointers and references)
• Sequence Of (Not in the language today)
• Ability to extend
• Usage semantics R/W, optional/required,

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Requirements for SMIng

• Textual representation
• Graphical views helpful but not ASCII (outside of
  the language)
• Ability to combine and group classes
• For scoping
• Set of classes/associations that are logically
  instantiated/manipulated together
• Containment of class/instance within another
• Object oriented baggage

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Class Information

• Class name
• Attributes
• Events
• Methods (Not in the language today)
• Not read/write or constructor/destructor but
  behavior and operations such as reset device and
  synchronize with foo
• Return value, In/Out parameters
• Without methods, potential to confuse return
  values and parameters with attributes, and
  obfuscate real semantics

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Inheritance

• From general (abstract) to specific
• Single inheritance
• Organizes and gives semantics to concepts
• Allows reuse (versus redefinition) of concepts
• Does there need to be a single root for all
  derived classes?

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Associations

• Relationships between classes/instances
• Can take the form of classes w/ pointer/reference
  attributes
• Multiplicity constraints (many to many, one to
  one, one to many, etc.) (Not in the language
  today)

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Constraints

• Attribute bounds and enumerations
• Usage - Read/Write, Optional vs. Required
• Semantic constraints (Not in the language today)
• Constraints for creating/deleting classes and
  associations (A must be associated with 1 (B OR
  C) A must be deleted if B is deleted)
• Constraints for transactional dependencies (A and
  B must be modified together)
• Interdependencies/relationships between
  attributes (for example, x,y coordinates) (Not in
  the language today)

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Requirements Missing in SMIng Proposal (and Other
Questions)

• Should SMIng describe info models?
• Support for associations
• Is it just a class with two (or more) pointers,
  allowing definition of data specific to the
  relationship?
• Primitives to convey cardinality
• Support for methods
• Sequence Of
• Semantic constraints
• Ability to distinguish classes as abstract/very
  general vs concrete/instantiable
• Others?