AOP/cross-cutting

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AOP/cross-cutting

• What is an aspect?

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What is an aspect?

• An aspect is a modular unit that cross-cuts other
  modular units.
• What means cross-cutting?
• Apply AOP to AOP. Tease an aspect apart into
  three units ideal graph, labels on nodes and
  edges of ideal graph, application to concrete
  graph using connectors specifies cross-cutting

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What is an aspect?

• An aspect is a modular unit that cross-cuts other
  modular units.
• Example MU 1 application code, MU 2 class
  library code. Application code uses names from
  class library. Cross-cutting.
• MU 1 is an aspect! Not reasonable
• What is missing?

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What is an aspect?

• An aspect is a modular unit that cross-cuts and
  enhances other modular units.
• Previous example now ruled out.
• Example MU 1 APPC, MU 2 class graph.
  Cross-cutting is indirect through a connector.
  APPC is an aspect

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Alternative definition
Stand-alone requiring context in order to
function

• An aspect
• is a modular unit that has no stand-alone
  function and
• that affects other modular units

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Other definition (Xerox PARC)

• Implement properties. Some are implemented by
  generalized procedures. Those that are not
  implemented by generalized procedures are called
  aspects.
• Aspects are defined modulo programming language
  and a set of components

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Terminology

• Building block BB
• Participants (classes at basic level) BB of
  type 1
• APPC BB of type 2 consisting of set of
  generic BB of type 1.
• Connectors map generic BB implements
  cross-cutting

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AOP

• components building blocks type 1
• whatever does not fit into one building block of
  type 1 is expressed as one building block type 2
  that consists of a set of generic building blocks
  of type 1.
• generic building blocks of a building block of
  type 2 are mapped to building blocks of type 1.

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Generic BB

• A building block with holes

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AOP

• Properties of mapping
• one generic building block is mapped to one or
  more building blocks
• building blocks may have parts. One part of
  generic building block is mapped to one or more
  parts of corresponding generic building block.

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Example APPCs

• Ideal graph participant graph
• Labels on nodes and edges participant code
• Concrete graph participant graph or application
  class graph
• Connectors specify cross-cutting

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Something missing in APPCs

• Components, connectors
• Components
• provided, required interface
• required interface includes participant graph
• participant code
• also needs help from other components that are
  connected to local participants

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Improved APPCs

• Components
• provided, required interface
• required interface includes participant graph
• participant code
• list of imported components
• connectors

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LoggingPricing
Interface of Pricing becomes interface of
LoggingPricing
Logging
Pricing
Summing
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CountingLocking
Interface of Counting becomes interface of
CountingLocking
Locking
Counting
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Visitors and components?

• component Summing
• participant Source
• Target t
• int sum() cg.traverse(this, new
• Strategy(from Source to Target),
• new Visitor int sum s start()s0
• void before(Target host) shost.what
• participant Target
• public int what

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Example

• Have component for Pricing
• Want to log instance creation of three
  participant classes. Use Logging component and
  connect to three participants

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Cross-cutting

• Does not only mean inserting aspect code into
  enhanced unit.
• There is interaction between aspect code and
  modified unit code. Some aspects can change
  structure of modified unit others just insert
  additional code into old structure

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Theory of cross cutting

• Model programs as graphs (e.g. class diagrams,
  abstract syntax trees, etc.)
• Aspects model as graph editing instructions
  modeled with respect to an ideal graph.
• Graph editing add new nodes and edges and add to
  node labels and edge labels

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Specifying cross-cutting

• Uniform node to nodes, edge to edges simple
  weaving
• explicit A,B,C,D
• succinct Nodes(Graph(From A to D))
• Non-uniform edge to multiple edges code is
  different from target edge to target edge

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Specifying cross-cuttingmapping

• With traversal. From A to B B mapped to multiple
  targets
• Without traversal. Two classes A and B with some
  connection? Without traversal is an uninteresting
  special case? Name map is the cross-cutting.

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Use of traversal strategiesto specify
cross-cutting in AOP

• Set of classes Nodes(strategy)
• Graph refinement map participant graph