  We supply a detailed proof of the result by P.S. Green and T.
H$\ddot{\text{u}}$bsch that all complete intersection Calabi--Yau 3-folds in
product of projective spaces are connected through projective conifold
transitions (known as the standard web). We also introduce a subclass of small
transitions which we call primitive small transitions and study such subclass.
More precisely, given a small projective resolution $\pi : \widehat{X}
\rightarrow X$ of a Calabi--Yau 3-fold $X$, we show that if the natural closed
immersion $Def(\widehat{X}) \hookrightarrow Def(X)$ is an isomorphism then $X$
has only ODPs as singularities.
