Is it necessary to set the itemtype attribute in microdata?

Question

HTML

Is it necessary to specify the itemtype in order to use microdata correctly?
That is, you need it like this:

<dd itemprop="address" itemscope
itemtype="http://data-vocabulary.org/Address">
<span itemprop="street-address">100 Main Street</span>
</dd>

or you can do it like this:

<dd itemprop="address" itemscope>
<span itemprop="street-address">100 Main Street</span>
</dd>