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Object-Relational Mapping

The software paradigm that is best suited to represent and manipulate population data is object-oriented programming (OOP). On the other hand, input and output data (especially in complex projects) are best stored in a relational database. Unfortunately, database relational modelling is less intuitive than OOP and requires a specific language (SQL) to retrieve and modify data.

In JAS-mine the interaction between the simulation and the (input and output) data is inspired to Object-Relational Mapping (ORM), a programming approach that facilitates the integration of object-oriented software systems with relational databases. An ORM product (JAS-mine uses Hibernate) constructs an object-oriented interface to provide services on data persistence, while abstracting at the same time from the implementation characteristics of the specific RDBMS (database management software) used. The management of input data persistence layers and simulation results is performed using standard database management tools, and the platform takes care of the automatic translation of the relational model (which is typical of a database) into the object-oriented simulation model, where each category of individuals or objects that populate the model is represented by a specific class, with its own properties and methods.

Hibernate Position

The main advantages of using an ORM system are:
  1. the masking of the implementation of the relational model in an object-oriented model;
  2. high portability compared to the DBMS technology adopted: no need to rewrite data input queries on database when changing DBMS, simply modify a few lines in the configuration of the ORM used;
  3. a drastic reduction in the amount of code to be written; the ORM masks behind simple commands the complex activities of data creation, extraction, update and deletion. These activities take up a considerable percentage of the time required for writing, testing and maintenance. Moreover they are inherently repetitive, thus increasing the chance of errors when writing the implementation code.
The most common ORM products available today offer a number of functions that would otherwise be performed manually by the programmer; in particular, the operations of loading the object graph based on association links defined at language level, and reading/writing/deleting are entirely automated. For instance, loading an instance of the Student class may result in the automatic loading of data concerning the student’s exam grades.

The use of an ORM facilitates the achievement of higher quality software standards, improving in particular its correctness, maintainability, potential evolutions and portability. On the down side, choosing an ORM paradigm introduces a software layer that impacts on performance, an aspect that is relevant to data-intensive applications like simulations. Translating the entity-relational model that is typical of a database into an object-based model requires additional activities that may slow down data upload and reading. Given the continuous increases in the speed and power of modern computers, we opted for a lean architectural structure even at the cost of slowing down the simulation engine.