Question irrelevance and discourse incoherence are important and typical problems in multi-document summarization especially when dealing with informal and opinionated texts. To address these two issues, we propose a domain-independent query-based extractive summarization approach for opinionated documents that uses intra-sentential discourse structures in the framework of schemata. To validate our approach, we have built a system named BlogSum and have evaluated its performance for question relevance and coherence using different datasets. Evaluation results indicate that the use of discourse relations combined with text schemas can effectively reduce question irrelevance and discourse incoherence even with informal and opinionated documents.