ISO/IEC 18025:2014 provides mechanisms to specify unambiguously objects used to model environmental concepts. To accomplish this, a collection of nine EDCS dictionaries of environmental concepts are specified:

1. classifications: specify the type of environmental objects;
2. attributes: specify the state of environmental objects;
3. attribute value characteristics: specify information concerning the values of attributes;
4. attribute enumerants: specify the allowable values for the state of an enumerated attribute;
5. units: specify quantitative measures of the state of some environmental objects;
6. unit scales: allow a wide range of numerical values to be stated;
7. unit equivalence classes: specify sets of units that are mutually comparable;
8. organizational schemas: useful for locating classifications and attributes sharing a common context; and
9. groups: into which concepts sharing a common context are collected.

A functional interface is also specified.

As denoting and encoding a concept requires a standard way of identifying the concept, ISO/IEC 18025:2014 specifies labels and codes in the dictionaries.

ISO/IEC 18025:2014 specifies environmental phenomena in categories that include, but are not limited to, the following:

1. abstract concepts (e.g., absolute latitude accuracy, geodetic azimuth);
2. airborne particulates and aerosols (e.g., cloud, dust, fog, snow);
3. animals (e.g., civilian, fish, human, whale pod);
4. atmosphere and atmospheric conditions (e.g., air temperature, humidity, rain rate, sensible and latent heat, wind speed and direction);
5. bathymetric physiography (e.g., bar, channel, continental shelf, guyot, reef, seamount, waterbody floor region);
6. electromagnetic and acoustic phenomena (e.g., acoustic noise, frequency, polarization, sound speed profile, surface reflectivity);
7. equipment (e.g., aircraft, spacecraft, tent, train, vessel);
8. extraterrestrial phenomena (e.g., asteroid, comet, planet);
9. hydrology (e.g., lake, rapids, river, swamp);
10. ice (e.g., iceberg, ice field, ice peak, ice shelf, glacier);
11. man-made structures and their interiors (e.g., bridge, building, hallway, road, room, tower);
12. ocean and littoral surface phenomena (e.g., beach profile, current, surf, tide, wave);
13. ocean floor (e.g., coral, rock, sand);
14. oceanographic conditions (e.g., luminescence, salinity, specific gravity, turbidity, water current speed);
15. physiography (e.g., cliff, gorge, island, mountain, reef, strait, valley region);
16. space (e.g., charged particle species, ionospheric scintillation, magnetic field, particle density, solar flares);
17. surface materials (e.g., concrete, metal, paint, soil); and
18. vegetation (e.g., crop land, forest, grass land, kelp bed, tree).