In this paper, we provide an overview of state-of-the-art research issues and achievements in the field of analytics over big data, and we extend the discussion to analytics over big multidimensional data as well, by highlighting open problems and actual research trends. Our analytical contribution is finally completed by several novel research directions arising in this field, which plays a leading role in next-generation Data Warehousing and OLAP research.

In this paper, we highlight open problems and actual research trends in the field of Data Warehousing and OLAP over Big Data, an emerging term in Data Warehousing and OLAP research. We also derive several novel research directions arising in this field, and put emphasis on possible contributions to be achieved by future research efforts.

We analyze a case study in the field of smart agriculture exploiting Explainable AI (XAI) approach, a field of study that aims to provide interpretations and explanations to the behaviour of AI systems. The study regards a multiclass classification problem on the Crop Recommendation dataset. The original task is the prediction of the most adequate crop, according to seven features. In addition to the predictions, two of the most well-known XAI approaches have been used in order to obtain explanations and interpretations of the behaviour of the models: SHAP (SHapley Additive ExPlanations), and LIME (Local Interpretable Model-Agnostic Explanations). Both packages provide easy-to-understand visualizations that allow common users to understand explanations of single predictions even without going into the mathematical details of the algorithms. Within the scientific community criticisms have been raised against these approaches, and recently some papers brought to light some weaknesses. However, the two algorithms are among the most popular in XAI and are still considered points of reference for this field of study.

In recent years, artificial intelligence (AI) and its subarea of deep learning have drawn the attention of many researchers. At the same time, advances in technologies enable the generation or collection of large amounts of valuable data (e.g., sensor data) from various sources in different applications, such as those for the Internet of Things (IoT), which in turn aims towards the development of smart cities. With the availability of sensor data from various sources, sensor information fusion is in demand for effective integration of big data. In this article, we present an AI-based sensor-information fusion system for supporting deep supervised learning of transportation data generated and collected from various types of sensors, including remote sensed imagery for the geographic information system (GIS), accelerometers, as well as sensors for the global navigation satellite system (GNSS) and global positioning system (GPS). The discovered knowledge and information returned from our system provides analysts with a clearer understanding of trajectories or mobility of citizens, which in turn helps to develop better transportation models to achieve the ultimate goal of smarter cities. Evaluation results show the effectiveness and practicality of our AI-based sensor information fusion system for supporting deep supervised learning of big transportation data.