  The problems of determining the minimum-sized \emph{identifying},
\emph{locating-dominating} and \emph{open locating-dominating codes} of an
input graph are special search problems that are challenging from both
theoretical and computational viewpoints. In these problems, one selects a
dominating set $C$ of a graph $G$ such that the vertices of a chosen subset of
$V(G)$ (i.e. either $V(G)\setminus C$ or $V(G)$ itself) are uniquely determined
by their neighborhoods in $C$. A typical line of attack for these problems is
to determine tight bounds for the minimum codes in various graphs classes. In
this work, we present tight lower and upper bounds for all three types of codes
for \emph{block graphs} (i.e. diamond-free chordal graphs). Our bounds are in
terms of the number of maximal cliques (or \emph{blocks}) of a block graph and
the order of the graph. Two of our upper bounds verify conjectures from the
literature - with one of them being now proven for block graphs in this
article. As for the lower bounds, we prove them to be linear in terms of both
the number of blocks and the order of the block graph. We provide examples of
families of block graphs whose minimum codes attain these bounds, thus showing
each bound to be tight.

Combinatorics;Discrete Mathematics