JESS - JOINT EXPERT SPECIATION SYSTEM
The concept of a chemical species is fundamental to JESS and to the JESS Thermodynamic Database.
Information about species is used to categorize all the thermodynamic data stored by JESS (so you can easily locate things).
Every species in the JESS Thermodynamic Database is represented by a symbol. For example, the ion of Zinc(II) has the symbol Zn+2 (in which, conventionally, the element's chemical abbreviation is followed by the ion's signed electronic charge).
Symbols like Zn+2 are called 'primitive' to indicate that they are a basic building-block of the database.
For convenience, it is also possible to describe species in terms of combinations of primitive symbols. In such cases, the symbol is referred to as a 'composite'. In constructing a composite symbol, you simply append the appropriate primitive symbols together, separating them from one another with underscore characters, _.
For example, the 1:1 complex formed between zinc(II) and ethylenediaminetetraacetate has the symbol Zn+2_EDTA-4 and this can protonate to form Zn+2_EDTA-4_H+1.