  We discuss the canonical form for a pure state of three identical bosons in
two modes, and classify its entanglement correlation into two types, the
analogous GHZ and the W types as well known in a system of three
distinguishable qubits. We have performed a detailed study of two important
entanglement measures for such a system, the concurrence $\mathcal{C}$ and the
triple entanglement measure $\tau$. We have also calculated explicitly the spin
squeezing parameter $\xi$ and the result shows that the W state is the most
``anti-squeezing'' state, for which the spin squeezing parameter cannot be
regarded as an entanglement measure.
