Next: Planning System Components
Up: Planning I
Previous: Search in Planning
What is the Blocks World? -- The world consists of:
- A flat surface such
as a tabletop
- An adequate set of identical blocks which are identified by
letters.
- The blocks can be stacked one on one to form towers of apparently
unlimited height.
- The stacking is achieved using a robot arm which has
fundamental operations and states which can be assessed using logic and combined
using logical operations.
- The robot can hold one block at a time and only one
block can be moved at a time.
We shall use the four actions:
- UNSTACK(A,B)
- -- pick up clear block A from block B;
- STACK(A,B)
- -- place block A using the arm onto clear block B;
- PICKUP(A)
- -- lift clear
block A with the empty arm;
- PUTDOWN(A)
- -- place the held block A onto a free space
on the table.
and the five predicates:
- ON(A,B)
- -- block A is on block B.
- ONTABLE(A)
- -- block A is on the table.
- CLEAR(A)
- -- block A has nothing on it.
- HOLDING(A)
- -- the arm
holds block A.
- ARMEMPTY
- -- the arm holds nothing.
Using logic but not logical notation we can say that If the arm is holding a
block it is not empty If block A is on the table it is not on any other block If
block A is on block B,block B is not clear.
Why Use the Blocks world as an example?
The blocks world is chosen because:
- it is sufficiently
simple and well behaved.
- easily understood
- yet still provides a good sample environment to study planning:
- problems can be
broken into nearly distinct subproblems
- we can
show how partial solutions need to be combined to form a realistic
complete solution.
Next: Planning System Components
Up: Planning I
Previous: Search in Planning
dave@cs.cf.ac.uk