The paper develops an abstract (over-approximating) semantics for double-pushout rewriting of graphs and graph-like objects. The focus is on the socalled materialization of left-hand sides from abstract graphs, a central concept in previous work. The first contribution is an accessible, general explanation of how materializations arise from universal properties and categorical constructions, in particular partial map classifiers, in a topos. Second, we introduce an extension by enriching objects with annotations and give a precise characterization of strongest post-conditions, which are effectively computable under certain assumptions.Abstract interpretation [12] is a fundamental static analysis technique that applies not only to conventional programs but also to general infinite-state systems. Shape analysis [32], a specific instance of abstract interpretation, pioneered an approach for analyzing pointer structures that keeps track of information about the "heap topology", e.g., out-degrees or existence of certain paths. One central idea of shape analysis is materialization, which arises as companion operation to summarizing distinct objects that share relevant properties. Materialization, a.k.a. partial concretization, is also fundamental in verification approaches based on separation logic [6,5,25], where it is also known as rearrangement [28], a special case of frame inference. Shape analysis-construed in a wide sense-has been adapted to graph transformation [31], a general purpose modelling language for systems with dynamically evolving topology, such as network protocols and cyber-physical systems. Motivated by earlier work of shape analysis for graph transformation [33,4,1,2,30,29], we want to put the materialization operation on a new footing, widening the scope of shape analysis.A natural abstraction mechanism for transition systems with graphs as states "summarizes" all graphs over a specific shape graph. Thus a single graph is used as abstraction ⋆ Partially supported by AFOSR.⊳ A rewriting formalism for graph abstractions that lifts the rule-based rewriting from single graphs to abstract graphs; it is developed for (abstract) objects in a topos.⊳ We characterize the materialization operation for abstract objects in a topos in terms of partial map classifiers, giving a sound and complete description of all occurrences of right-hand sides of rules obtained by rewriting an abstract object.→ Sec. 3 ⊳ We decorate abstract objects with annotations from an ordered monoid and extend abstract rewriting to abstract objects with annotations. For the specific case of graphs, we consider global annotations (counting the nodes and edges in a graph), local annotations (constraining the degree of a node), and path annotations (constraining the existence of paths between certain nodes). → Sec. 4 ⊳ We show that abstract rewriting with annotations is sound and, with additional assumptions, complete. Finally, we even derive strongest post-conditions for the case of graph rewriting with annotations. → Sec. 5Related work: ...