For an ordered k-decomposition D = {G1, G2, . . . , Gk} of a connected graph G and an edge e of G, the D-code of e is the k-tuple cD(e) = (d(e, G1), d(e, G2), . . . , d(e, Gk)), where d(e, Gi) is the distance from e to Gi . A decomposition D is resolving if every two distinct edges of G have distinct D-codes. The minimum k for which G has a resolving k-decomposition is its decomposition dimension dimd(G). A resolving decomposition D of G is connected if each Gi is connected for 1 ≤ i ≤ k. The minimum k for which G has a connected resolving k-decomposition is its connected decomposition number cd(G). Thus 2 ≤ dimd(G) ≤ cd(G) ≤ m for every connected graph G of size m ≥ 2. All nontrivial connected graphs with connected decomposition number 2 or m are characterized. We provide bounds for the connected decomposition number of a connected graph in terms of its size, diameter, girth, and other parameters. A formula for the connected decomposition number of a nonpath tree is established. It is shown that, for every pair a, b of integers with 3 ≤ a ≤ b, there exists a connected graph G with dimd(G) = a and cd(G) = b.
For an ordered $k$-decomposition $\mathcal D = \lbrace G_1, G_2,\dots , G_k\rbrace $ of a connected graph $G$ and an edge $e$ of $G$, the $\mathcal D$-code of $e$ is the $k$-tuple $c_{\mathcal D}(e) = (d(e, G_1), d(e, G_2),\ldots , d(e, G_k))$, where $d(e, G_i)$ is the distance from $e$ to $G_i$. A decomposition $\mathcal D$ is resolving if every two distinct edges of $G$ have distinct $\mathcal D$-codes. The minimum $k$ for which $G$ has a resolving $k$-decomposition is its decomposition dimension $\dim _d(G)$. A resolving decomposition $\mathcal D$ of $G$ is connected if each $G_i$ is connected for $1 \le i \le k$. The minimum $k$ for which $G$ has a connected resolving $k$-decomposition is its connected decomposition number $\mathop {\mathrm cd}(G)$. Thus $2 \le \dim _d(G) \le \mathop {\mathrm cd}(G) \le m$ for every connected graph $G$ of size $m \ge 2$. All nontrivial connected graphs of size $m$ with connected decomposition number 2 or $m$ have been characterized. We present characterizations for connected graphs of size $m$ with connected decomposition number $m-1$ or $m-2$. It is shown that each pair $s, t$ of rational numbers with $ 0 < s \le t \le 1$, there is a connected graph $G$ of size $m$ such that $\dim _d(G)/m = s$ and $\mathop {\mathrm cd}(G) / m = t$.