There are various ways in which we can classify. Below are some of the classifications:

• Major: A defect, which will cause an observable product failure or departure from requirements.
• Minor: A defect that will not cause a failure in execution of the product.
• Fatal: A defect that will cause the system to crash or close abruptly or effect other applications.

Work product wise:

• SSD: A defect from System Study document
• FSD: A defect from Functional Specification document
• ADS: A defect from Architectural Design Document
• DDS: A defect from Detailed Design document
• Source code: A defect from Source code
• Test Plan/ Test Cases: A defect from Test Plan/ Test Cases
• User Documentation: A defect from User manuals, Operating manuals

Type of Errors Wise:

• Comments: Inadequate/ incorrect/ misleading or missing comments in the source code
• Computational Error: Improper computation of the formulae / improper business validations in code.
• Data error: Incorrect data population / update in database
• Database Error: Error in the database schema/Design
• Missing Design: Design features/approach missed/not documented in the design document and hence does not correspond to requirements
• Inadequate or sub optimal Design: Design features/approach needs additional inputs for it to be completeDesign features described does not provide the best approach (optimal approach) towards the solution required
• In correct Design: Wrong or inaccurate Design
• Ambiguous Design: Design feature/approach is not clear to the reviewer. Also includes ambiguous use of words or unclear design features.
• Boundary Conditions Neglected: Boundary conditions not addressed/incorrect
• Interface Error: Internal or external to application interfacing error, Incorrect handling of passing parameters, Incorrect alignment, incorrect/misplaced fields/objects, un friendly window/screen positions
• Logic Error: Missing or Inadequate or irrelevant or ambiguous functionality in source code
• Message Error: Inadequate/ incorrect/ misleading or missing error messages in source code
• Navigation Error: Navigation not coded correctly in source code
• Performance Error: An error related to performance/optimality of the code
• Missing Requirements: Implicit/Explicit requirements are missed/not documented during requirement phase
• Inadequate Requirements: Requirement needs additional inputs for to be complete
• Incorrect Requirements: Wrong or inaccurate requirements
• Ambiguous Requirements: Requirement is not clear to the reviewer. Also includes ambiguous use of words – e.g. Like, such as, may be, could be, might etc.
• Sequencing / Timing Error: Error due to incorrect/missing consideration to timeouts and improper/missing sequencing in source code.
• Standards: Standards not followed like improper exception handling, use of E & D Formats and project related design/requirements/coding standards
• System Error: Hardware and Operating System related error, Memory leak
• Test Plan / Cases Error: Inadequate/ incorrect/ ambiguous or duplicate or missing - Test Plan/ Test Cases & Test Scripts, Incorrect/Incomplete test setup
• Typographical Error: Spelling / Grammar mistake in documents/source code
• Variable Declaration Error: Improper declaration / usage of variables, Type mismatch error in source code

Status Wise:

• Open
• Closed
• Deferred
• Cancelled

These are the major ways in which defects can be classified. I'll write more regarding the probable causes of these defects in one of my next posts... :)

Also See:

• Bug Report
• Bug Life Cycle
• Software Errors
• Bug Report Template

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