R help - May 2006 - Why random item need grouping symbol '|' ? And why is there no '|' in fixed item in lme?

Hi everyone,

What's the difference between the following two linear mixed models?
Supposed productivity scores is decided by three types of machines as used
by six different workers.

scoreij=workeri+machinej+eij   i=1,2,...6   j=1,2,3

machine = as.factor(machine)
worker = as.factor(worker)
lme(fixed=score~machine, data=example1, random=~1|worker)

My question is what is the difference between the above lme and the
following lme? Why is there no '|' in fixed item in lme?

lme(fixed=score~machine, data=example1, random=~worker)