Procedural Design

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Procedural Design

• February 2001
• Janet Murray

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What is a Computer?
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What is a Computer?

• A device or system that is capable of carrying
  out a sequence of operations in a distinctly and
  explicitly defined manner.
• - Oxford Dictionary of Computing

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What is a Computer?

• A device or system that is capable of carrying
  out a sequence of operations in a distinctly and
  explicitly defined manner.
• - Oxford Dictionary of Computing

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Primitives

• Not capable of being broken down into simpler
  form. (Oxford Dictionary of Computing)
• E.g. arithmetical primitives
• ASCII code
• on/off bits

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Computation and Complexity

• The central problem for computer science is to
  develop methods for handling complexity. The two
  techniques that have proven most effective are
  finding the best representation for the problem
  and decomposing it into smaller parts.
• - Biermann, Great Ideas in Computer Science

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Lego - like Design

• Primitives the first layer in increasingly
  complex structure
• Building complexity by nesting abstractions
• arithmetic operators square roots quadratic
  equations
• ascii code compare strings read /
  retrieve/display information search database
• Like the human mind
• chair kitchen room home
• move limbs drive use map go to mall

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Abstraction

• The principle of ignoring those aspects of a
  subject that are not relevant to the current
  purpose in order to concentrate on those that
  are.
• - Oxford Dictionary of Computing

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Data Abstraction

• The principle of defining a data type in terms of
  the operations that apply to objects of the type
  with the constraint that the values of such
  objects can be modified and observed only by use
  of those operations.
• - Oxford Dictionary of Computing

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Procedural Abstraction

• The principle that any operation that achieves a
  well-defined effect can be treated by its users
  as a single entity, despite the fact that the
  operation may actually be achieved by some
  sequence of lower level operations. e.g. Pascal
  subroutines, Director custom behaviors
• - Oxford Dictionary of Computing

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Information Hiding (encapsulation)

• A principle, used when developing an overall
  program structure that each component should
  encapsulate or hide a single design decision.
  Parnas method of preparing a list of tricky and
  changeable design decision elements, and make
  each one its own module interface to module
  hides specifics of processing, so does not
  change.
• - Oxford Dictionary of Computing

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Modularity

• Modular programming A style of programming in
  which the complete program is decomposed into a
  set of components called modules.usually refers
  to Parnas idea of promoting information
  hiding now usually on object oriented
  principles
• - Oxford Dictionary of Computing

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Object

• an identifiable component of a software
  systemthat is in some sense self-contained.an
  instance of a component comprising data
  structures and procedures (called methods) for
  manipulating the structures. The methods
  behaviors in Director are activitated by
  messages sent to the object
• - Oxford Dictionary of Computing

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Object continued

• The methods behaviors in Director are
  activitated by messages sent to the object, and
  the interior structure of the object is entirely
  hidden from any other object (a property called
  encapsulation).
• - Oxford Dictionary of Computing

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Object Class

• Objects are derived from a template, and the
  collection of objects that are instances of a
  particular template are said to form a class.
• - Oxford Dictionary of Computing

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Object Inheritance

• A particularly important feature is inheritance
  which allows new classes to be defined in terms
  of existing classes, inheriting some or all of
  the properties of an existing class. if more
  than one parent allowed, it is called multiple
  inheritance
• - Oxford Dictionary of Computing

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Declarative vs Procedural Knowledge

• Describes something
• Recipe in words
• Choreographic notes

• Does something
• Recipe in action
• The dance itself

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Model vs Simulation

• Describes the structure and behavior

• Embodies the structure and behavior

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Procedural

• I am using it as opposite of declarative as
  referring to behavior, to actions
• I am NOT using it to refer to the difference
  between Pascal and C (NOT meant as opposite of
  object oriented, but as INCLUDING object oriented
  and older style programming environments)

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Algorithm vs Heuristic

• Exactly specified procedure
• Contains all the knowledge you need to process
  any instance of the data
• Useful for rote tasks like payrolls
• How computers do things

• Rule of thumb
• Dependent on domain knowledge that cannot yet be
  represented
• Necessary for travelling salesman like problems
• How people do things (being analog)

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Group Exercise 1

• Specify a procedure for making breakfast

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Group Exercise 1

• Specify a procedure for making breakfast
• Abstraction (what is ignored?)
• Encapsulation (what is black boxed)
• Templates (does it account for drip coffee and
  instant coffee? For tea?)
• Cultural constructions? What do you assume?
• Modularity? Are there messages or parameters
  passed between distinct activities?

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Group Exercise 2

• Make a family of autonomous characters
• Take the family through a day together
• Modularity
• divide up the work and coordinate it
• What do you need to know about other peoples
  modules?

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Autonomous Agents

• Agent (Oxford) An autonomous system that
  receives information from its environment,
  processes it, and performs actions on the
  environment.
• E.g. the dogz and catz in pfmagics Petz series

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Emergence

• Behavior that arises from systems that are made
  up of multiple autonomous elements and therefore
  give rise to results that could not be
  specifically determined.
• E.g. we cant know exactly how a particular dog
  and cat will play together because too many
  factors are involved artificial life phenomena
  such as flocking

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State

• A composite of variables within a system that
  define the current configuration the state of a
  system will effect the range of possible
  responses to the same input. For example, a
  virtual character in a hungry state will show
  more interest in food. A container in an empty
  state will be able to receive contents.

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