The contents of the working memory represent what the system `knows' about the problem at any one moment. At the start, this is the initial knowledge state, which is transformed into a new state each time an operator (production rule) is applied. At its simplest, working memory can be represented as a simple database of facts -- for example,
[birdcage is open]
[tweetie is in birdcage]
[sylvester is in room]
At any one time the size of working memory is usually very small, just as the number of distinct items that the human mind can hold in short-term memory is small.