Decomposition Reactions
The result of a combination reaction can be reversed; in other words, a compound can be decomposed into the components from which it was formed. This type of reaction is called a decomposition reaction. Many decomposition reactions occur via oxidation-reduction as illustrated below.
But many other decomposition reactions do not involve a corresponding oxidation and reduction of the substances as shown below.

Note, that in this example of chemical decomposition, the oxidation states of the elements involved remain constant.