# The Prerequisite of Software Architecture I Learned from Code Complete


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# Software Architecture
* Describe in single document
* Close to the requirement
* Design constraints that apply systemwide
* Change of the architecture is expensive during the construction
# Typical Architectural Components
* If you are building the whole system yourself, your work on the architecture will overlap your work on the more detailed design
* If the architecture is designed by someone, you should be able to find the important components by yourself
## Program Organization
* The architecture provides the rationale for the system organization and show that each class has been carefully considered
* The architecture should define the major building blocks in a program
	* single class
	* subsystem consisting of many class
	* routine work together on high level function
* Building block should have one area of responsibility
* Minimizing what each building block knows about other building blocks
* The communication rules for each building block should be well defined
## Major Class
* Identify the responsibilities of each major class
* Specify the 20 percent of the class that make up 80 percent of the system behavior
## Data Design
* Data should normally be accessed directly by only one subsystem or class
* It should describe alternatives that were considered and justify the choices that were made.
## Business Rules
* If the architecture depends on the specific business rule, the impact to the system from it should be described
## User Interface Design
* Should be specified in the software architecture
* The architecture should be modularized so that a new user interface can be substituted without effect the business rules and output of the program
## Resource Management
* Memory constraint
* Network connections
## Security
* Rules for handling untrusted data
	* user input
	* cookies
	* configuration
* Encryption
* Level of detail contained in error messages
* Protect secrete data in memory
## Performance
* Speed vs memory
* Space and time budgets for each class or object
## Scalability
* Ability of a system to grow to meet future of the demands
	* Number of user
	* Number of server
	* Size of database record
	* Number of network nodes
* If the system is not expected to grow and scalability is not the issue
## Interoperability
* Share data or resource with other software or hardware should be described
## I18n
* program to support multiple locales
## Error Processing
* One of the thorniest problem
* Handle them consistently should be spelled out in the architecture
* Is error corrective or merely detective?
* How does the program propagate error?
	* Immediately discard the data that caused the error and enter the error processing state
	* Wait until all the process complete
* What are the conventions for handling error messages?
* Level of responsibility of each class
	* Each class validate their own data
	* Group of class responsible for validate the data
	* Can class at any level assume that the data received are clean?
## Fault Tolerance
* The architecture should indicate the kind of fault tolerance expected
## Architectural Feasibility
* If infeasible in any area could render the project unworkable, the architecture should indicate how those issues have been investigate through PoC or research
* These risk should be resolved before full-scale construction begin
## Overengineering
* An architecture specifies a more robust system than that specified by the requirement
## Buy vs Build Decisions
* The most radical solution to build software is not to build it at all
	* buy it instead
	* use open-source
* If the architecture isn't using off the shelf components, it should explain how self built component surpass ready make libraries and components
## Change Strategy
* Making the architecture flexible enough to accommodate likely changes
* The strategy for handling change should be described
## General Architecture Quality
* The problem with large system is to maintain the conceptual integrity and consistency
* Good software architecture is largely machine and language independent
* Identify the risk