Wireless　sensor　networks　(WSNs)　are　widely　used　in　many　application　fields.　Because　sensor　nodes　are　generally　battery　powered,　to　prolong　network　lifetime,　energy　conservation　becomes　a　major　concern　in　answering　queries　over　sensor　networks.　In　addition,　a　robust　and　fault-tolerant　data-collection　method　is　highly　desirable　against　a　lossy　network　with　low-quality　wireless　communication　links　and　unreliable　sensor　nodes.　We　propose　a　signature-file-based　approach　to　approximately　answer　queries　over　WSNs.　By　combining　the　duplicate-insensitive　structure　of　signature　files　and　the　redundant　multipath　routing　approach,　we　create　a　robust　in-network　aggregation　scheme,　which　can　answer　both　aggregative　and　range　queries　with　high　accuracy　while　significantly　reducing　the　cost　of　message　transmissions.　Simulations　have　been　conducted　to　evaluate　the　performance　of　this　approach　under　various　network　conditions.　Compared　with　previous　solutions,　our　signature-file-based　approach　achieves　the　highest　accuracy　under　reasonable　energy　cost.