House Designer

House Designer
Using Knowledge Based Engineering
and Lisp to automatically design
buildings
Kristoffer Kvello
SELVAAG
© Selvaag 2008
1
Sunday, August 13, 2017
Table of contents
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House Designer (what is it?)
Why Lisp?
Knowledge Based Engineering
Libraries we use
Use of Screamer by House Designer
Some thoughts about using Lisp for this
Users
The company
• Selvaag
• One of Norway’s ten largest construction
companies
• Around 700 employees
• Selvaag Bluethink
• Daughter company writing software
• 24 employees
The company
• The Lisp-team
– 6 developers
• one of which is the primary author of Movitz and
Binary-Types
– http://common-lisp.net/project/movitz/
– http://www.cs.uit.no/~frodef/sw/binary-types/
House Designer
• System for automatic design of apartments and
buildings
• Based on sketches from architect/engineer, the
system calculates the consequences and fleshes out
the design
• And analyzes the results:
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cost
statics
heat transfer
light conditions
Main benefits
• The problem:
– In designing buildings there is an enormous amount of detail that
needs to be remembered and taken into account
– Consequently, errors are often made, leading to costly repairs
– Due to the same reason, experimenting with new ideas is time
consuming and costly
• House Designer aids the architect by taking care of all aspects
that are considered ”mechanical” (”all” is long-term goal)
– reduces errors
– allows quick what-if analyses
– automatically produces documentation
One view of the system
CAD system
s-expr
User Interface (java)
(ca. 75K LOC)
xml
House Designer code
(ca. 288K LOC)
Finite element analysis
Design++
Costing engine
database
Lisp (Franz’ ACL)
wall types, wall offsets,
wall junctions
Where doors are needed,
door types, door
positions, hinge sides,
door directions
Amount, types and
positioning of required
electrical fixtures
A valid piping layout
(water and ventilation),
ensuring that the building
is possible to construct
Number of windows
required, types, positions
Wheelchair maneouvre
space, ensuring that the
layout meets government
regulations
Wall extension, automatically
generated in order to cover the
sofa
Open plan
Sofa
Why Lisp?
• The use of Lisp was a top management
decision from the start
• The company wanted a system to automate
knowledge
• The search led to a methodology called
Knowledge Based Engineering, and early KBE
systems were based on Lisp
• The KBE company emphasised the power of
Lisp
Knowledge Based Engineering
• Today KBE has come to mean many things (check
wikipedia)
• Best analogy is ”object oriented spreadsheet tightly
coupled to a CAD-system”
• Provides handling of dependencies and recalculates
what is implicated by a change, just like a
spreadsheet
• Lisp projects that seem very similar:
• Cells
• http://common-lisp.net/project/cells/
• Computed-Class
• http://common-lisp.net/project/computed-class/
Lisp based KBE tools
• Design++ (recently bought by Bentley
Systems)
– http://dp.com/
• GDL
– http://www.genworks.com/
Examples of rules –
how to calculate the area of various objects
The area of a window is its
width times its height
The area of an apartment is
the sum of the area of its
internal spaces
The area of an access
balcony section is the area it
has as a normal space, plus
the sum of its lips
Libraries we use
• asdf
– http://cclan.cvs.sourceforge.net/cclan/asdf/
• zip
– http://common-lisp.net/project/zip/
• clsql 3.6.6
– http://clsql.b9.com
• Slime
– http://common-lisp.net/project/slime/
Libraries we use
• cl-utilities
– http://common-lisp.net/project/cl-utilities/
• s-xml
– http://common-lisp.net/project/s-xml/
• aserve
– http://opensource.franz.com/aserve/index.html
• expresso 3.1.0
– http://exp-engine.sourceforge.net/
• screamer 3.24.1
– http://clocc.sourceforge.net/clocc/src/screamer/
The problem of essentially
cyclic relationships
• We have encountered problem domains that are
essentially cyclic: there is no natural place to start
– positioning of walls, since they are all connected across
floors horizontally and vertically
– placement of piping in the service shaft
– outlay of prefabricated floor elements
• Engineers start at an arbitrary place and iterate until
they find a good solution
• We found we needed backtracking
– We also wanted to just start somewhere and get a solution
by trial & error
The problem of essentially
cyclic relationships
• The solution was to use Screamer
– Ordinary KBE rules create walls based on the
”nominal” borders of spaces
– Constraint variables are set up that...
• assert that all walls are aligned with the others they
meet
• assert that certain rooms must have a certain area
• assert that certain walls (e.g. in vertical shafts) fit each
other vertically
• assert that equpment has sufficient wall space
The problem of essentially
cyclic relationships
• All these constraints are
expressed as demands for offset
on each wall from its ”nominal”
line, i.e. as numeric variables
• The total set of constraints is
handed over to Screamer
– Backtracking occurs within what is
to us a black box
• When Screamer is done, each
wall will find its values in a table,
and the KBE system proceeds as
normal
The problem of essentially
cyclic relationships
• Piping: part of the
problem is
establishing how
many pipes you need
• Positioning of piping
in the service shaft
uses Screamer’s
backtracking
explicitly in the
House Designer
code: (either 1 2 ..)
The problem of essentially
cyclic relationships
• Not all constraints
are necessarily
satisfied
• We prioritize them
and arrange for the
ones with the lowest
priority to fail first
• House Designer
informs the user
which constraints
failed
Some thoughts about using Lisp for this
• Highlights of what we most appreciate with
Lisp:
– interactivity: quick recompile, with a living model.
No need to re-run program to reach same state
– the break-loop: debugger with restarts
– reader macros, allowing us to customize the
syntax of the tool to our liking
Modified syntax
New syntax, defined by
means of a reader macro
Original syntax of the KBE tool
Some thoughts about using Lisp for this
• What we most like (cont.)
– advice, to customize the tool further
– the ease with which one can examine the lisp
image and find out how things work
– handler-bind
• Lisp has never been a problem, neither
regarding lack of functionality/libraries nor
getting the necessary people
Users
• One of our sister companies uses House Designer for
statics reports
– That branch of the science of mechanics concerned with
forces acting on bodies in equilibrium
• Another sister company is using it to establish
consequences of modified governmental regulations
• We are in the process of delivering House Designer
to a construction company in the EU
Questions?