NF-SS: A Normal Form for Semistructured Schema

Abstract

Abstract. Semistructured data is becoming increasingly important for web applications with the development of XML and related technologies. Designing a "good" semistructured database is crucial to prevent data redundancy, inconsistency and undesirable updating anomalies. However, unlike relational databases, there is no normalization theory to facilitate the design of good semistructured databases. In this paper, we introduce the notion of a semistructured schema and identify the various anomalies that may occur in such a schema. A Normal Form for Semistructured Schemata, NF-SS, is proposed. A semistructured schema in NF-SS guarantees minimal redundancy and hence no undesirable updating anomalies for the associated semistructured databases. Furthermore, a semistructured schema in NF-SS gives a more reasonable representation of real world semantics. We develop an iterative algorithm based on a set of heuristic rules to restructure a semistructured schema into a normal form. These design methods also provide insights into the normalization task for semistructured databases.

Theorem prover approach to semistructured data design

“…In addition, we evaluated our approach against the normalization examples presented in Arenas [3] and Wu [52]'s papers. These normalization algorithms transform a schema of semistructured data into one that satisfies the associated normal form defined to avoid data redundancies.…”

“…In the research presented by Wu et al [52], a normalization algorithm is developed to minimize data redundancies in XML documents. A Normal Form for Semistructured Schemata (NF-SS) is defined using DTD represented in a tree like structure and extended functional dependency (EFD), where EFD is defined by combining functional dependencies and key constraints together.…”

“…Normalization is the process of analyzing and restructuring a database schema in order to minimize redundancies in data instances. A number of normalization processes have been defined for semistructured database systems including [3,20,52], which transform a schema based on the keys and functional dependencies. Although the processes are different, there are common operations for transforming the structure, such as creating a reference for an object class, moving an attribute to another object class, and swapping an object class with another object class.…”

“…Moreover, we also generated the examples of incorrectly designed schema transformation and verified them to further evaluate our solution. A transformation that is lossless but not dependency preserving was generated and verified using the PVS theorem [52]'s algorithm, do not necessarily guarantee functional dependencies between attributes are preserved in their schema transformation. Additionally, a transformation that is neither dependency preserving nor lossless was generated and verified.…”

“…They transform the schema of the semistructured data with redundancy into a better form. For example, currently proposed normalization algorithms include the normal form for semistructured data (NF-SS) developed by Wu et al [52], XML normal form (XNF) developed by Embley and Mok [20], and normal form for XML documents developed by Arenas and Libkin [3]. Such normalization algorithms should always preserve data integrity.…”