Loss of data semantics in syntax directed translation
Donald B. Sanderson · 1994
A greater demand for automated data and the increasing complexity of data models have altered the focus of data from restructuring data to preserving its semantic meaning. The goal of this thesis is to consider the issues involved in semantic loss in data translation, specifically during syntactically directed translation. A framework for examining information loss during is required as ad-hoc has too many variable factors for algorithmic prediction of semantic loss. Therefore a translation as system is used. This involves import and export mappings to a neutral model, and the use of a schema migration system in the neutral model to effect the translation. If a rich neutral model is chosen then the syntactic and semantic impact of the import and export mappings are minimal. This requires classifying the different features in data modelling languages and specifying the types and behaviors of migration functions needed for any given neutral model. Next the semantics of the stored data needs to be recorded. A synthesis of existing semantic data models is used. The semantics are then linked with the features of the data modelling language that denotes them. Using these techniques, it is possible to predict for a given data modelling language what types of semantics it will support and also predict many of the semantic effects caused by its migration functions. A prototype system is developed using the ROSE 3.0 implementation of EXPRESS as a proof of concept. The prototype is tested with several short examples and one large example. The conclusions drawn are that the basic approach is sound but can be improved. Semantic loss, such as the destruction of relationships or loss of constraints on a data type, can be predicted based on syntactically specified migration functions. However, this approach cannot predict the creation of semantic information when new data types are introduced nor can it differentiate between semantic schemas which are identical in definition but differ in meaning. To address these issues several syntactical operations need to be combined to form semantic migration functions. Work on this extension to the prototype is proposed.