**4.2 Conceptualization of model**

The model is built using an input - process - output model (see **Figure 1**). Input consists of controllable input and uncontrollable input. Meanwhile, the output consists of the desirable output and the undesirable output. Feedback will also be analyzed thoroughly. To facilitate organization, the model will be divided into several sub-models, each sub-model will be further divided into several sub sub-models.

The model consists of 5 subsystems: 1) Plant (Crop), 2) Soil, 3) Land, 4) Environment, and 5) OPPS. The interaction of the five subsystems is presented in **Figure 2**.

Model input – proses - output will be applied. Input of this model consists of all parameters related to the all components (see **Table 1**). While output this model involves both expected outputs and unexpected output.

The model that has been developed, validated and mutually agreed upon will then be used to assess aspects of crop productivity, soil quality, land and environment as well as OPPS in various types of oil palm plantations in Indonesia.

**Figure 1.** *Model input – Proses – Output of OPPS model.*

*Necessity, Principle and Technique of Evaluation Model to Assess Sustainability of Oil Palm… DOI: http://dx.doi.org/10.5772/intechopen.98585*

**Figure 2.**

*Subsystem components of oil palm plantation system and their interactions.*


#### **Table 1.**

*Component variables and management of each sub-system.*
