The aim of this chapter is not be a general introduction to smart contracts. For such an introduction, Nick Szabo's 'The Idea of Smart Contracts' is recommended, as are the Etherum Community resources avaliable online. This chapter discusses a tangible, technical realisation of financial transcations made via smart contracts.
Within the first contract, the profit aims and parameters, the funding goal, the period of the crowdsale, and the price of the terra0 tokens are laid out. If Ether is transferred to the contract, it automatically returns the approriate amount of terra0 tokens. The crowdsale phase ends after the defined time period, providing the necessary capital for the project initiators to set up the project. The contract therefore uses tokens and the transfer function of the second contract. The first contract is very similar to the standarized crowdsale contract published in the below referenced Ethereum documentation:9
The second contract administers the in- and outputs of the forest, and further serves as its real 'owner'. It functions as an automated trade centre for tokens. The contract defines two different tokens:
terra0 token function as a debenture. The token can be acquired only during the crowdsale phase and represents a share of the property of the smart contract. The terra0 token can be sold to the contract by its owner for Ether.
The Woodtoken is created by the initialization of the contracts, and remains as a stock with the contract, and is acquired from the contract in exchange for Ether.
The Woodtoken can be seen an agreed amount of wood that can be harvested in the process of self-aquisation (Selbstwerberverfahren). The amount for sale, as well as the price of the tokens, are recalcuated twice annually.
Furthermore, the contract calculates the specific trees which can be felled, and from this, the total amount of avaliable wood. This function is executed via accessing the Oracle, which transmits topical data such as growth rate, age, number, and type of the trees to the smart contract. This function is executed every six months by the Etherum clock. A more detailed explanation of the functionality of the Oracle and the clock follow in 5.1.3, as does an explanation of the data analysis procedure on the aquired satellite pictures. The function fixes the amount of Woodtokens to be sold; the contract thus contains a simple feedback system.
9. Crowdsale: Raising Funds From Friends Without A Third Party, 28.07.2016, https://ethereum.org, URL: https://ethereum.org/crowdsale ↩