A two-layer cloud database model and its bidirectional conversion algorithms

The existed cloud data models can not well meet the management requirements of structured data including a great deal of relational data, therefore a two-layer cloud data model consisting of a presentation layer and a storage layer is proposed. In the presentation layer, the conception of composite class and composite object are defined to represent the structure and the data of structured data respectively. In the storage layer, a composite class in the presentation layer is transformed into a 3-tuple which preserves data structure in mappings between composite attributes and their sub-attributes by using a rule set; and a composite object in the presentation layer is transformed into another 3-tuple which preserves a structured data set in simple objects without embed objects by using a CAO (Component-Attribute-Object) set in which each element mainly consists of a simple object and the identification of its father object. In order to store data in key-value model, a method to convert a CAO to a pair of key-value is proposed. Furthermore, two algorithms were proposed to convert data between the representation layer and the storage layer. Data experiment shows the two conversion algorithms are effective. The proposed model is fit for the management requirements of structured data in the cloud because composite object can represent structured data and avoid join operation of relation data and CAO can be stored in key-value model.