Robert C.Martin wrote an interesting article about a set of metrics that can be used to measure the quality of an object-oriented design in terms of the interdependence between the subsystems of that design.
Here’s from the article what he said about the interdependence between modules:
What is it that makes a design rigid, fragile and difficult to reuse. It is the interdependence of the subsystems within that design. A design is rigid if it cannot be easily changed. Such rigidity is due to the fact that a single change to heavily interdependent software begins a cascade of changes in dependent modules. When the extent of that cascade of change cannot be predicted by the designers or maintainers the impact of the change cannot be estimated. This makes the cost of the change impossible to estimate. Managers, faced with such unpredictability, become reluctant to authorize changes. Thus the design becomes rigid.
Relational database management systems are the most commonly used system to store and use data, but for extremely large amounts of data, this kind of system doesn’t scale up properly.
The concept of “NoSQL”(Not Only SQL) has been spreading due to the growing demand for relational database alternatives. The biggest motivation behind NoSQL is scalability. NoSQL solutions can offer a way to store and use extremely large amounts of data, but with less overhead, less work, better performance, and less downtime.