[R] Why random item need grouping symbol '|' ? And why is there no '|' in fixed item in lme?

[fanzhang2 at gmail.com]

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)