So Why Software Architecture

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So --- Why Software Architecture?

• As software systems continue to grow in size and
  complexity (both breadth and depth), just looking
  at algorithms and data structures is not enough.
• Large systems, by definition, is made of many
  sub-components that interact with each other.

Coding
Design
Architecture
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Software Architecture

• Your Text A systems architecture is the set
  of principal design decisions made during its
  development and any subsequent evolution.
• Tsui modifies it to say A systems
  architecture is the result of a set of principal
  design decisions made and documented (in design
  document, code, etc.) during its development and
  subsequent evolution
• There is no standard definition of software
  architecture, yet there are more definitions in
  Chapter 3 of your text

What do you all think ?
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A Definition from McMaster Univ. (Canada)

• Architectural Design (the designing activity)
• The process of i) identifying the components
  and
• ii) establishing a framework for control and
  communications of these components
• Software Architecture (the product from
  designing)
• The documented output from the architectural
  design activities.

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Architecture-Centric

• Architecture-Centric approach to software
  development places an emphasis on design with
  an aim for
• Good quality (e.g. defects) and many
  attributes
• Cost-effective development
• High leveraging of past experiences

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Analogy to Physical Building

• Software architecture and physical building
  architecture similarities
• Architecture exist independently from, but
  strongly linked to, the (building) code
• Properties of the (structures) software are
  induced by the design of their architecture
• The architect needs to have broad skills beyond
  just (construction) programming
• Architecture is more important than the process
  of (building activities) software development
  activities
• Architecture has matured into a discipline of its
  own with many architectural (building) design
  styles. (this one may be questionable)

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Architectural Styles

• In physical building there are
• Gothic style
• Ranch style
• Bavarian Chalet style
• Italian Villa style
• English Tudor style
• etc.
• In software we have
• Layered style
• Pipe Filter style
• etc.

Style is a set of constraints placed on the
design to achieve certain properties
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Some Differences from Physical Building

• Buildings have been around for a much longer time
  than software so a lot less is known about
  software
• Software does not have a medium such as
  materials of wood, stone, etc. for physical
  building so software is not as visible
• Software is more malleable than a physical
  building so software changes are more frequent,
  later in development stage, bigger in magnitude.

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from Roman Architect Vitruvius to Todays
Software Designer Mitch Kapor (not in your text)

• Paraphrasing (Vitruvius)
• ---- well-designed buildings were those which
  exhibited firmness, commodity, and delight -----
• Paraphrasing (Mitch Kapor-lotus 1-2-3) for
  software we want similar characteristics
• firmness No Bugs (or less bugs)
• commodity functionalities that satisfy the
  requirements
• delight pleasurable experience (usage
  experience)
• Paraphrasing (Winograd-Stanford U.)
• --- architects and designers work with
  commodity and delight, and the engineers works
  with firmness ----

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Why the Big emphasis on Architecture?

• Giving architecture the deserved attention
  provides
• Conceptual integrity
• A basis for reuse of ---- knowledge, experience,
  design, and code
• Effective project communication
• Management of families of systems
• Architecture must be considered the heart of
  developing software system, even
• More than processes and methodologies
• More than programming
• More than requirements analysis (Tsui objects
  to this one you?)

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World Wide Web ---- Needs Architectural
Description

• What is the web?
• Multiple ways to describe it depending on the
  view
• Set of independent resources, interconnected by
  computing systems, that provide some services
• Set of computing programs that interact with each
  other according to a set of rules specified in
  standards and protocols such as HTTP, XML, etc.
• Set of interactions of agents and servers through
  interconnected systems .
• None of these views, even with diagrams, would
  give us a deep understanding of what the web is.
  But we can not get into all the details because
  it would need close to infinite amount of
  descriptions to explain all the programs, all
  protocols, all data, etc.
• Thus we need to describe the rules (decisions)
  by which the main parts work and interact ----
  use architectural style ?

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Observations made in trying to describe the World
Wide Web

• The architecture of the Web is totally separate
  from the code that implements all the various
  parts. (One needs to describe the Web at an
  architectural level.)
• There is no single piece of code that
  implements the web, and thus neither its
  architecture.
• There are multiple, equivalent pieces of code
  that exist and implement various components of
  the Web.
• The stylistic constraints that constitute the
  definition of the Web is not apparent in any one
  piece of the code, but the effects as implemented
  in all the pieces are evident in the Web.

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a specific Architectural Style Pipe and filter

• Main components
• Filter processes a stream of input-data to
  produce some out- put data
• Pipe a conduit that allows the flow of data

read input file
process file
filter
This architecture style focuses on the dynamic
(interaction) and forces a fairly simple,
sequential structure
pipe
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Pipe and Filter UNIX Influence

• UNIX command line processing of the pipe symbol,
  l
• the output from the command to the left of
  the symbol, l, is to be sent as input to the
  command to the right of the pipe
• this mechanism got rid of specifying a file
  as std output of a command and then specifying
  that same file as the std input to another
  command, including possibly removing this
  intermediate file afterwards

Example ( UNIX commands) cat my.txt I
live in the city of Atlanta cat my.txt I sed
s/i/o/g I love on the coty of Atlanta
Example Assume that in the file called
my.txt is the following I live in the city of
Atlanta
Note the pipe symbol, l
First cat command outputs my.txt to screen. The
second cat command reads my.txt and sends it to
sed command which search for i and globally
replace it with o. You can have more l and
other processing commands, such as sort, to form
a sophisticated software.
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Architecture critical for ---- Product Family

• Software Product family is a set of related
  software components which has
• i) some common components and
• ii) some variable components
• The variable components provide, for each product
  within the family, the differentiator by
  features, by cost (price), by time, etc.
• Reuse and cost sharing is the big advantage of
  Product Family (in reality ---- schedule also
  played a part)

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Product Family ---- and Versioning
General Requirements (Version 3)
General Requirements (Version 2)
US (common) code v3
General Requirements
US (common) code v2
French ( version 3 )
If Fench Version 2.1 came after Version 3, we
may need to build a French V3.1
US (common) code v1
French ( version 2 )
French ( version 1 )
Japanese ( version 3 )
French (version 2.1)
Japanese ( version 2 )
Japanese ( version 1 )
Brazilian ( version 3)
Brazilian ( version 2 )
Brazilian ( version 1 )
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Summarizing Arch Design We Should Ask

• What are the major functional components of the
  architecture?
• Decompose the requirements
• Synthesize similar functionalities into major
  components
• Decompose the major components into subcomponents
• How are the components related?
• Structure of relationship under static condition
• Dynamic flow of control and data during execution
• What elements are needed to facilitate the
  architecture?
• Connector elements introduced to bring in
  versatile interaction
• Additional functional components introduced to
  improve a particular attribute (e.g. security,
  availability)
• How do we design and evaluate various
  non-functional behavioral properties?
• Performance, security, maintainability,
  availability, etc. needs to be defined,
  specified, measured.
• What execution environment/platform needs to be
  considered and resolved?
• Is there any over-riding constraint (e.g. style)
  that should be invariant?