Skip to main content

Ecosystem development: from process-oriented to object-oriented system

One of my recent projects is to develop a three-dimensional coupled water and carbon cycle ecosystem model. After finished the first version of the system, I wasn't quite satisfied with the system architecture, partly due to the complexity of the system dependency.

In fact, I have spent great amount of time trying to design the system to be well-structured. Using class in C++11, I have defined many classes to controls different types of algorithms and processes. 

The interesting part of the story started to unveil when I started to write/revise the manuscript. When I tried to explain the conceptual model, I realized that even though the current system has use object-oriented programming (OOP) approach through class, most components within the system are not actually using the OOP concept at all. In a word, the system still acts like a process-oriented program.

Taking a review of several other Earth system models (e.g., Community Land Model), I realized that unfortunately most of current models fall into this catalog, process-oriented instead of object-oriented system. 

Process-oriented system usually focuses on "action" instead of "object". For example, we focus on "photosynthesis" process but not the entry where it actually takes place. As this traditional approach is more intuitive to us, it usually causes problems in program development such as low reusability due to dependency.

Another problem arises in my own research is that process-oriented approach cannot handle interactions between processes/objects very well, at least not as intuitive as they are supposed to be. In lots of times, we are looking into the relationship between different species, or more generally, types of objects or individuals. In this scenario, an object-oriented approach will significantly improve the readability and efficiency in model development. And usually it may simply help us to understand some scientific questions.

In fact, in many fields (e.g., Artificial Intelligence) object-oriented approach is been widely used. In climate change, we are also using similar concepts such as "feedbacks" and "butterfly effects". However, we have not yet truly treat our Earth system as individual objects so far.

Comments

Popular posts from this blog

Spatial datasets operations: mask raster using region of interest

Climate change related studies usually involve spatial datasets extraction from a larger domain.
In this article, I will briefly discuss some potential issues and solutions.

In the most common scenario, we need to extract a raster file using a polygon based shapefile. And I will focus as an example.

In a typical desktop application such as ArcMap or ENVI, this is usually done with a tool called clip or extract using mask or ROI.

Before any analysis can be done, it is the best practice to project all datasets into the same projection.

If you are lucky enough, you may find that the polygon you will use actually matches up with the raster grid perfectly. But it rarely happens unless you created the shapefile using "fishnet" or other approaches.

What if luck is not with you? The algorithm within these tool usually will make the best estimate of the value based on the location. The nearest re-sample, but not limited to, will be used to calculate the value. But what about the outp…

Numerical simulation: ode/pde solver and spin-up

For Earth Science model development, I inevitably have to deal with ODE and PDE equations. I also have come across some discussion related to this topic, i.e.,

https://www.researchgate.net/post/What_does_one_mean_by_Model_Spin_Up_Time

In an attempt to answer this question, as well as redefine the problem I am dealing with, I decided to organize some materials to illustrate our current state on this topic.

Models are essentially equations. In Earth Science, these equations are usually ODE or PDE. So I want to discuss this from a mathematical perspective.

Ideally, we want to solve these ODE/PDE with initial condition (IC) and boundary condition (BC) using various numerical methods.
https://en.wikipedia.org/wiki/Initial_value_problem
https://en.wikipedia.org/wiki/Boundary_value_problem

Because of the nature of geology, everything is similar to its neighbors. So we can construct a system of equations which may have multiple equation for each single grid cell. Now we have an array of equation…

Watershed Delineation On A Hexagonal Mesh Grid: Part A

One of our recent publications is "Watershed Delineation On A Hexagonal Mesh Grid" published on Environmental Modeling and Software (link).
Here I want to provide some behind the scene details of this study.

(The figures are high resolution, you might need to zoom in to view.)

First, I'd like to introduce the motivation of this work. Many of us including me have done lots of watershed/catchment hydrology modeling. For example, one of my recent publications is a three-dimensional carbon-water cycle modeling work (link), which uses lots of watershed hydrology algorithms.
In principle, watershed hydrology should be applied to large spatial domain, even global scale. But why no one is doing it?  I will use the popular USDA SWAT model as an example. Why no one is setting up a SWAT model globally? 
There are several reasons we cannot use SWAT at global scale: We cannot produce a global DEM with a desired map projection. SWAT model relies on stream network, which depends on DEM.…