Technology tree

In strategy computer games, of both the turn-based and real-time varieties, a tech tree, short for "technology tree," is an abstract hierarchical visual representation of the possible paths of research a player can take.

Typically, at the beginning of a session of a strategy game, a player may only have a few options for technologies to research. Each technology that a player researches will open up more options, but may or may not, depending on the computer game the player is playing, close off the paths to other options. The tech tree is the representation of all possible paths of research a player can take. A tech tree appears visually similar to a tree, with many branches, because technological research in these games tend not to be linear. Technically, however, the tech tree is not a tree, according to the graph theory definition, as often two or more parents share a child. Rather, tech trees are usually better classified as directed acyclic graphs.

A player who is engaged in research activities is said to be "teching up," "going up the tech tree," or "moving up the tech tree." Experienced players of a game will likely be aware of all possible branches of the tech tree for that game, as knowing what options specific choices of research open up allows the player to make fast and informed decisions on what to build or research, translating into a significant advantage over players with less knowledge of the tech tree for that game. Analysis of a tech tree can lead players to memorize and use specific build orders.

Tech trees are implemented in various ways. StarCraft, for instance, has different tech trees for each race, although each entry typically has a close analogue in another race (the Terran Goliath, Zerg Hydralisk, and Protoss Dragoon are all ground-based, ranged attack units). Age of Empires, on the other hand, has a single tech tree for all civilizations, but certain civilizations cannot access certain elements of it. This is compensated for with advances in other areas; so while the Egyptians cannot access advanced academy or siege units, they have bonuses for farming. This makes race selection much more tactical. Alternatively, Civilization allows all races to access the whole of the same tree, but different civilizations may be given certain technologies immediately and there is a full choice as to how you advance (science, political, military, etc).

Philosophy

A technology tree in a game raises a distinct implicit perspective, which may or may not be realistic:

• Higher levels of technology are always advantageous. Typically, this translates to a boost in economic growth, a boost in destructiveness of the military, a boost in the endurance of friendly units to damage or, very occasionally, victory itself.
• Progress occurs by paradigm shifts, and not by gradual evolution. Research gives usually no rewards, until a certain stage is reached. A new upgrade replaces the previous version absolutely, and instantly. However, in some games, such as The Lord of the Rings: The Battle for Middle Earth, Homeworld: Cataclysm, or Pax Imperia: Eminent Domain every unit needs to upgrade itself before it is able to utilize the new technologies.
• Scientific breakthroughs are predictable. Devoting additional resources to research will always lead to a proportionate increase in the rate of progress. Conversely, devoting no resources to research will lead to complete stagnation.
• Research is target-led. While some games (e.g., Sid Meier's Alpha Centauri) allow vague fields of research to be set, most employ a system by which a technology is chosen, and research proceeds until it is attained.
• The cost of progress increases. Higher level research items take more resources to research than lower level ones.
• This increase in the cost of progress is counter to the concept inherent in the technological singularity, which is modelled on an accelerating pace of progress. This can be and is compensated for both by making each advancement greater than comparable past advancements, and in turn based games, by reducing the span between terms (e.g. the Civilization series turns lasting 20 years early on, slowly reducing to 1 year every turn).