Lixiao Zheng

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When transforming data one often wants certain information in the data source to be preserved, i.e., we identify parts of the source data and require these parts to be transformed without loss of information. We characterize the preservation of selected information in terms of the notions of invertibility and query preservation, in a setting when(More)
The problem of answering queries using views arises in a wide variety of data management applications. From the information-theoretic perspective, a notion of <i>determinacy</i> has been recently introduced to formalize the intuitive notion that whether a set of views <i>V</i> is sufficient to answer a query <i>Q.</i> We say that <i>V determines Q</i> iff(More)
One simple approach to testing grammars is to derive a number of sentences from the grammar under test and to validate whether they comply with the intended language. Purdom has proposed a by-now folklore sentence generation algorithm which however suffers from the fact that the sentences generated are usually too few and some of them are long with(More)
Producing sentences from a grammar, according to various criteria, is required in many applications. It is also a basic building block for grammar engineering. This paper presents a toolkit for context-free grammars, which mainly consists of several algorithms for sentence generation or enumeration and for coverage analysis for context-free grammars. The(More)
Grammars, especially context-free grammars, are widely used within and even outside the field of computer science. In this paper, we present a systematic framework for grammar testing, in which some commonly used techniques for testing programs such as module testing and integration testing are adapted and applied to the testing of grammars. We propose a(More)
In this paper, we investigate the complexity of deciding determinism of unary languages. First, we give a method to derive a set of arithmetic progressions from a regular expression E over a unary alphabet, and establish relations between numbers represented by these arithmetic progressions and words in L(E). Next, we define a problem relating to arithmetic(More)
In order to build a practical mini OA system for small and medium enterprise, key business, overall requirement, functional requirements and non-functional requirements of Yardi Kooboo (Xiamen) Technology Co. Ltd. Are analyzed after understanding the company's specific workflow and management processes. Following software engineering, the entire progress of(More)
研究一类含有通配符 (*)、 递归 (//)和分支 ([]) 操作的 XPath 查询语句的视图确定性和重写完全性问题。 证明出该类 XPath 语句的视图确定性问题是 coNP 难的, 并且该类语句是重写不完全的。 进而从语义和语法两个角度给出视图 V 确定查询 Q 的一系列必要条件, 以及一个判定视图确定性问题的非完全算法。 证明出对于一类特殊的 XPath 子类, 即只含有通配符和分支操作的 XPath 子类, 视图确定性问题可以在多项式时间内判定。 同时指出该子类的重写完全语言, 并给出一个从视图中计算查询结果的有效方法。
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