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IN SEARCH OF THE SOFTWARE URSATZ Sean Cribbs @seancribbs

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ABOUT ME Software Engineer at Basho Technologies We make Riak! erstwhile Pianist, Conductor, Composer, Music Theorist

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IN SEARCH OF... An understanding of so!ware cra!smanship An intuitive technique for analysis of software structure A subjective means of critical comparison More why and less how

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WHY CARE? We can improve our cra!, so we need a "amework for critical thought that goes beyond surface features. There is a difference between simplicity and ease. My belief: Systems reflect [leak?] the foundations on which they are built.

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A TALE OF TWO PIECES images from Wikimedia Commons

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A TALE OF TWO PIECES images from Wikimedia Commons

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A TALE OF TWO PIECES images from Wikimedia Commons

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A TALE OF TWO PIECES J.S. Bach’s Prelude No. 1 in C and Chopin’s Etude No. 8 in F images from Wikimedia Commons

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A TALE OF TWO PIECES J.S. Bach’s Prelude No. 1 in C and Chopin’s Etude No. 8 in F Have the SAME Fundamental Structure images from Wikimedia Commons

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WHO IS HEINRICH SCHENKER?

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BIOGRAPHICAL Born 1868 in present-day Ukraine Studied as a child with Carl Mikuli in Lemberg (Lviv) Scholarship to University of Vienna in 1884, also studied at the Konservatorium with Anton Bruckner & Ernst Ludwig Became regular performer, conductor, composer, critic, and theorist Taught his theories privately in his home

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ACCOMPLISHMENTS Championed Urtext and the study of primary sources: manuscripts, diaries, letters Published extensive scholarly editions of major works, incl. Beethoven’s Symphony no. 9 Theories of Harmony, Counterpoint, and Free Composition

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SCHENKERIAN ANALYSIS & CODE

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HARMONIC SERIES a.k.a. “The Overtone Series” or “Chord of Nature” images from Wikimedia Commons

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HARMONIC SERIES a.k.a. “The Overtone Series” or “Chord of Nature” images from Wikimedia Commons

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HARMONIC SERIES a.k.a. “The Overtone Series” or “Chord of Nature” images from Wikimedia Commons

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VERTICAL IN CODE The environments in which our software runs – hardware, operating system, runtime, libraries – constitute the vertical dimension or harmony. Each component in the vertical is built on a layer below, imparting some of that layer’s aesthetics and form up the stack.

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COUNTERPOINT The interaction of two or more simultaneous melodic lines, aka “voice leading” Counterpoint “rules” derived from intervallic relationships, aesthetic considerations Strict: regular divisions of other line aka “species” Free: free choice of all/any divisions, chromaticism, freer dissonances

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HORIZONTAL IN CODE Linear progressions of steps in code are analogous to melody. Interactions and tensions between independent procedures constitute a sort of counterpoint. Procedures in lock-step are like strict counterpoint; procedures with independence are more free and pleasing.

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DER TONWILLE “The Will of the Tones”, or Scale Functions images from Wikimedia Commons 1 2 3 4 5 6 7 8 1 - tonic 2 - dissonant, down 3 - consonant 4 - dissonant, down 5 - consonant 6 - consonant, down 7 - dissonant, up 8 - consonant

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WILL OF THE CODE Coupling and connascence are analogous to notions of consonance, dissonance, and scale function. Removing coupling resolves unnecessary dissonance. Reducing the degree of connascence produces more harmonious, flexible, modular code. The relationships of independent procedures should point toward the same goal.

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URSATZ The Fundamental Structure images from Wikimedia Commons

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URSATZ The Fundamental Structure images from Wikimedia Commons

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URSATZ The Fundamental Structure images from Wikimedia Commons

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URSATZ The Fundamental Structure images from Wikimedia Commons

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URSATZ The Fundamental Structure images from Wikimedia Commons

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URSATZ The Fundamental Structure images from Wikimedia Commons

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PROLONGATION “Semper idem sed non eodom modo” Always the same, but not always in the same way. The process of composing-out [Auskomponierung]: extending a harmony over time, or elaboration The exploration of the meanings of a motif Gives rise to different structural levels (Schichte) Progression from strict to "ee counterpoint

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CODE PROLONGATION Refactoring toward general algorithms is analogous to structural prolongation in music. Use of generalized algorithms [patterns?] increases readability and maintainability, and can be more amenable to global optimization.

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CODE COMPLEXITY “Most techniques for controlling compleixty...decompose a problem into almost independently solvable subproblems” “[A] good package encapsulates a higher level concept which has meaning independent of its implementation.” “Often one can make progress to the solution of a simplified version of the problem which is similar in some essential aspect to the original one but which differs from it in detail.” – Sussman and Steele, The Art of the Interpreter

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GRAPHIC ANALYSIS “Urlinie Tafel” Image from http://nicolas.meeus.free.fr/Analyses.html

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CODE GRAPHS? We have no strong analogy here: boxes-and-arrows, sequence diagrams, UML, etc, are all in a vocabulary different "om the subject being analyzed. On the other hand, we%-structured code could approach its own graphical analysis.

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KEY POINTS A unique understanding of harmony and counterpoint Relies on the intuition and subjectivity of the musician Multiple, interrelated layers of structure via prolongation A common language independent of style

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LIMITATIONS Focused on Tonal music only, expanded later by others Plagued with 19th-century chauvinism, disregards unprivileged viewpoints Predates modernist and post-modernist art and theory

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EXAMPLE

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Client App riak_kv_pb_listener riak_kv_pb_server riak_kv_pb_server riak_kv_pb_server riak_kv_pb_server TCP Riak riak-erlang-client

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PROBLEMS Client library is a dependency of the server Hard to extend server process with new requests, coupled to Riak KV Request processing intermixed with connection handling

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DECOUPLING Separate request/response message definition into an independent library Separate connection management from request processing, using Erlang “behaviours” - basically creating a uniform interface Extract the new structure from Riak KV into a new namespace/app

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PATTERN ELABORATION gen gen_server riak_api_pb_server

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PATTERN ELABORATION gen gen_server riak_api_pb_server riak_api_pb_service riak_kv_pb_object

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PATTERN ELABORATION gen gen_server riak_api_pb_server riak_api_pb_service riak_kv_pb_object Implementation Behaviour

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REVIEW

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REVIEW Software and music are multi-layered with intricate internal relationships. Our cra! of software should reflect an intuition and awareness of multiple simultaneous levels of abstraction. We are both composer and analyst. This analytical technique does not prove greatness or correctness, but could be a means for greater insight into software design.

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REFERENCES Schenker, Heinrich; ed. and annot. Oswald Jonas (1954) [1906]. Harmony. trans. Elisabeth Mann-Borgese. Chicago: University of Chicago Press. ISBN 0-226-73734-9. OCLC 280916. Schenker, Heinrich. Five Graphic Music Analyses. Dover, 1969. SchenkerGUIDE http://www.schenkerguide.com Schenkerian analysis on Wikipedia: http://en.wikipedia.org/wiki/Schenkerian_analysis

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REFERENCES, CONT. Luciane Beduschi and Nicolas Meeùs. Schenkerian Theory and Analysis http://nicolas.meeus.free.fr/Analyses.html Steele, Guy and Sussman, Gerald. The Art of the Interpreter. MIT AI memo No. 453, 1978. ftp://publications.ai.mit.edu/ ai-publications/pdf/AIM-453.pdf

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THANK YOU @seancribbs