Stackless Processing of Streamed Trees

International audienceProcessing tree-structured data in the streaming model is a challenge: capturing regular properties of streamed trees by means of a stack is costly in memory, but falling back to finite-state automata drastically limits the computational power. We propose an intermediate stackless model based on register automata equipped with a single counter, used to maintain the current depth in the tree. We explore the power of this model to validate and query streamed trees. Our main result is an effective characterization of regular path queries (RPQs) that can be evaluated stacklessly-with and without registers. In particular, we confirm the conjectured characterization of tree languages defined by DTDs that are recognizable without registers, by Segoufin and Vianu (2002), in the special case of tree languages defined by means of an RPQ

Schema Validation via Streaming Circuits

International audienceXML schema validation can be performed in constant memory in the streaming model if and only if the schema admits only trees of bounded depth - an acceptable assumption from the practical view-point. In this paper we refine this analysis by taking into account that data can be streamed block-by-block, rather then letter-by-letter, which provides opportunities to speed up the computation by parallelizing the processing of each block. For this purpose we introduce the model of streaming circuits, which process words of arbitrary length in blocks of fixed size, passing constant amount of information between blocks. This model allows us to transfer fundamental results about the circuit complexity of regular languages to the setting of streaming schema validation, which leads to effective constructions of streaming circuits of depth logarithmic in the block size, or even constant under certain assumptions on the input schema. For nested-relational DTDs, a practically motivated class of bounded-depth XML schemas, we provide an efficient construction yielding constant-depth streaming circuits with particularly good parameters