This work reports on research conducted on the domain of multi-document summarization using background knowledge. The research focuses on summary evaluation and the implementation of a set of generic use tools for NLP tasks and especially for automatic summarization. Within this work we formalize the n-gram graph representation and its use in NLP tasks. We present the use of n-gram graphs for the tasks of summary evaluation, content selection, novelty detection and redundancy removal. Furthermore, we present a set of algorithmic constructs and methodologies, based on the notion of n-gram graphs, that aimto support meaning extraction and textual quality quantification.