Programmer Competency Matrix

Note that the knowledge for each level is cumulative; being at
level n implies that you also know everything from the
levels lower than n.

Computer Science

2n (Level 0)n2 (Level 1)n (Level 2)log(n) (Level 3)Comments
data structuresDoesn’t know the difference between Array and LinkedListAble to explain and use Arrays, LinkedLists, Dictionaries etc in practical programming tasksKnows space and time tradeoffs of the basic data structures, Arrays vs LinkedLists, Able to explain how hashtables can be implemented and can handle collisions, Priority queues and ways to implement them etc.Knowledge of advanced data structures like B-trees, binomial and fibonacci heaps, AVL/Red Black trees, Splay Trees, Skip Lists, tries etc.
algorithmsUnable to find the average of numbers in an array (It’s hard to believe but I’ve interviewed such candidates)Basic sorting, searching and data structure traversal and retrieval algorithmsTree, Graph, simple greedy and divide and conquer algorithms, is able to understand the relevance of the levels of this matrix.Able to recognize and code dynamic programming solutions, good knowledge of graph algorithms, good knowledge of numerical computation algorithms, able to identify NP problems etc.
systems programmingDoesn’t know what a compiler, linker or interpreter isBasic understanding of compilers, linker and interpreters. Understands what assembly code is and how things work at the hardware level. Some knowledge of virtual memory and paging.Understands kernel mode vs. user mode, multi-threading, synchronization primitives and how they’re implemented, able to read assembly code. Understands how networks work, understanding of network protocols and socket level programming.Understands the entire programming stack, hardware (CPU + Memory + Cache + Interrupts + microcode), binary code, assembly, static and dynamic linking, compilation, interpretation, JIT compilation, garbage collection, heap, stack, memory addressing…

Software Engineering

2n (Level 0)n2 (Level 1)n (Level 2)log(n) (Level 3)Comments
source code version controlFolder backups by dateVSS and beginning CVS/SVN userProficient in using CVS and SVN features. Knows how to branch and merge, use patches setup repository properties etc.Knowledge of distributed VCS systems. Has tried out Bzr/Mercurial/Darcs/Git
build automationOnly knows how to build from IDEKnows how to build the system from the command lineCan setup a script to build the basic systemCan setup a script to build the system and also documentation, installers, generate release notes and tag the code in source control
automated testingThinks that all testing is the job of the testerHas written automated unit tests and comes up with good unit test cases for the code that is being writtenHas written code in TDD mannerUnderstands and is able to setup automated functional, load/performance and UI tests


2n (Level 0)n2 (Level 1)n (Level 2)log(n) (Level 3)Comments
problem decompositionOnly straight line code with copy paste for reuseAble to break up problem into multiple functionsAble to come up with reusable functions/objects that solve the overall problemUse of appropriate data structures and algorithms and comes up with generic/object-oriented code that encapsulate aspects of the problem that are subject to change.
systems decompositionNot able to think above the level of a single file/classAble to break up problem space and design solution as long as it is within the same platform/technologyAble to design systems that span multiple technologies/platforms.Able to visualize and design complex systems with multiple product lines and integrations with external systems. Also should be able to design operations support systems like monitoring, reporting, fail overs etc.
communicationCannot express thoughts/ideas to peers. Poor spelling and grammar.Peers can understand what is being said. Good spelling and grammar.Is able to effectively communicate with peersAble to understand and communicate thoughts/design/ideas/specs in a unambiguous manner and adjusts communication as per the contextThis is an often under rated but very critical criteria for judging a programmer. With the increase in outsourcing of programming tasks to places where English is not the native tongue this issue has become more prominent. I know of several projects that failed because the programmers could not understand what the intent of the communication was.
code organization within a fileno evidence of organization within a fileMethods are grouped logically or by accessibilityCode is grouped into regions and well commented with references to other source filesFile has license header, summary, well commented, consistent white space usage. The file should look beautiful.
code organization across filesNo thought given to organizing code across filesRelated files are grouped into a folderEach physical file has a unique purpose, for e.g. one class definition, one feature implementation etc.Code organization at a physical level closely matches design and looking at file names and folder distribution provides insights into design
source tree organizationEverything in one folderBasic separation of code into logical folders.No circular dependencies, binaries, libs, docs, builds, third-party code all organized into appropriate foldersPhysical layout of source tree matches logical hierarchy and organization. The directory names and organization provide insights into the design of the system.The difference between this and the previous item is in the scale of organization, source tree organization relates to the entire set of artifacts that define the system.
code readabilityMono-syllable namesGood names for files, variables classes, methods etc.No long functions, comments explaining unusual code, bug fixes, code assumptionsCode assumptions are verified using asserts, code flows naturally – no deep nesting of conditionals or methods
defensive codingDoesn’t understand the conceptChecks all arguments and asserts critical assumptions in codeMakes sure to check return values and check for exceptions around code that can fail.Has his own library to help with defensive coding, writes unit tests that simulate faults
error handlingOnly codes the happy caseBasic error handling around code that can throw exceptions/generate errorsEnsures that error/exceptions leave program in good state, resources, connections and memory is all cleaned up properlyCodes to detect possible exception before, maintain consistent exception handling strategy in all layers of code, come up with guidelines on exception handling for entire system.
IDEMostly uses IDE for text editingKnows their way around the interface, able to effectively use the IDE using menus.Knows keyboard shortcuts for most used operations.Has written custom macros
APINeeds to look up the documentation frequentlyHas the most frequently used APIs in memoryVast and In-depth knowledge of the APIHas written libraries that sit on top of the API to simplify frequently used tasks and to fill in gaps in the APIE.g. of API can be Java library, .net framework or the custom API for the application
frameworksHas not used any framework outside of the core platformHas heard about but not used the popular frameworks available for the platform.Has used more than one framework in a professional capacity and is well-versed with the idioms of the frameworks.Author of framework
requirementsTakes the given requirements and codes to specCome up with questions regarding missed cases in the specUnderstand complete picture and come up with entire areas that need to be specedAble to suggest better alternatives and flows to given requirements based on experience
scriptingNo knowledge of scripting toolsBatch files/shell scriptsPerl/Python/Ruby/VBScript/PowershellHas written and published reusable code
databaseThinks that Excel is a databaseKnows basic database concepts, normalization, ACID, transactions and can write simple selectsAble to design good and normalized database schemas keeping in mind the queries that’ll have to be run, proficient in use of views, stored procedures, triggers and user defined types. Knows difference between clustered and non-clustered indexes. Proficient in use of ORM tools.Can do basic database administration, performance optimization, index optimization, write advanced select queries, able to replace cursor usage with relational sql, understands how data is stored internally, understands how indexes are stored internally, understands how databases can be mirrored, replicated etc. Understands how the two phase commit works.


2n (Level 0)n2 (Level 1)n (Level 2)log(n) (Level 3)Comments
languages with professional experienceImperative or Object OrientedImperative, Object-Oriented and declarative (SQL), added bonus if they understand static vs dynamic typing, weak vs strong typing and static inferred typesFunctional, added bonus if they understand lazy evaluation, currying, continuationsConcurrent (Erlang, Oz) and Logic (Prolog)
platforms with professional experience12-34-56+
years of professional experience12-56-910+
domain knowledgeNo knowledge of the domainHas worked on at least one product in the domain.Has worked on multiple products in the same domain.Domain expert. Has designed and implemented several products/solutions in the domain. Well versed with standard terms, protocols used in the domain.


tool knowledgeLimited to primary IDE (VS.Net, Eclipse etc.)Knows about some alternatives to popular and standard tools.Good knowledge of editors, debuggers, IDEs, open source alternatives etc. etc. For e.g. someone who knows most of the tools from Scott Hanselman’s power tools list. Has used ORM tools.Has actually written tools and scripts, added bonus if they’ve been published.
languages exposed toImperative or Object OrientedImperative, Object-Oriented and declarative (SQL), added bonus if they understand static vs dynamic typing, weak vs strong typing and static inferred typesFunctional, added bonus if they understand lazy evaluation, currying, continuationsConcurrent (Erlang, Oz) and Logic (Prolog)
codebase knowledgeHas never looked at the codebaseBasic knowledge of the code layout and how to build the systemGood working knowledge of code base, has implemented several bug fixes and maybe some small features.Has implemented multiple big features in the codebase and can easily visualize the changes required for most features or bug fixes.
knowledge of upcoming technologiesHas not heard of the upcoming technologiesHas heard of upcoming technologies in the fieldHas downloaded the alpha preview/CTP/beta and read some articles/manualsHas played with the previews and has actually built something with it and as a bonus shared that with everyone else
platform internalsZero knowledge of platform internalsHas basic knowledge of how the platform works internallyDeep knowledge of platform internals and can visualize how the platform takes the program and converts it into executable code.Has written tools to enhance or provide information on platform internals. For e.g. disassemblers, decompilers, debuggers etc.
booksUnleashed series, 21 days series, 24 hour series, dummies series…Code Complete, Don’t Make me Think, Mastering Regular ExpressionsDesign Patterns, Peopleware, Programming Pearls, Algorithm Design Manual, Pragmatic Programmer, Mythical Man monthStructure and Interpretation of Computer Programs, Concepts Techniques, Models of Computer Programming, Art of Computer Programming, Database systems , by C. J Date, Thinking Forth, Little Schemer
blogsHas heard of them but never got the time.Reads tech/programming/software engineering blogs and listens to podcasts regularly.Maintains a link blog with some collection of useful articles and tools that he/she has collectedMaintains a blog in which personal insights and thoughts on programming are shared