# Domino Connecting Games

This page is an expanded version of a section of Joe Celko's taxonomy of domino games.

Connecting games are what most people think of as typical domino games. Tiles are laid according to a matching rule, normally end to end or side to side, to create chains or trains of tiles that form the tableau for the game. This genus of games can be divided into smaller groups according to the different matching rules, the use of the undealt tiles or 'boneyard' the different shapes of layout, and the game objectives.

### A) Matching rules

These are rules that determine which tiles it is legal to add to the layout. Nearly all traditional domino connecting games use either equal end matching or matador matching.

1. Matching equal ends. This is by far the most common matching rule in use. The touching ends of the connected tiles must have equal numbers, like this:

2. Matador matching. The ends of the connected tiles must add up to a particular total. When playing with a [6:6] set, the total is 7, and in general with an [n:n] set, touching ends must add up to n+1. The double blank and tiles whose two ends add up to the required total are called matadors, and normally function as wild tiles which can be played next to any tile.

3. Other matching rules. Many other matching systems can be imagined, and several recently invented domino games use a variety of rules governing which tiles can be played where.

### B) Boneyard, drawing and discarding rules

The boneyard is the collection of tiles (if any) that remain after all players have drawn their initial hands.

In many games players can draw additional tiles from the boneyard at their turn to play. There are several possible versions of the rule in this case. For example:

1. A player who is unable to play from their hand must draw a tile from the boneyard. If unable to play after drawing they must pass.
2. A player who is unable to play must continue to draw tiles from the boneyard until either they are able to play or the boneyard is exhausted.

There are some games and some situations when a player who has no play cannot draw and simply passes their turn. For example:

1. In some games, all the tiles are dealt to the players. Since there is no boneyard there is no drawing.
2. In some games the boneyard tiles are set aside and cannot be drawn.
3. In some games a certain number of tiles - for example 2 - must remain out of play. When the boneyard is reduced to this size, there is no further drawing.

Games in which there is no boneyard are usually called Block games and those with a boneyard are called draw games for obvious reasons.

In Oriental connecting domino games there is generally no boneyard, and a player who is unable to add a tile to the layout must discard a tile, playing it face down in front of them. The pips on these discarded tiles count as penalty points and determine who has won the game. Games of this type are found in China, Korea and Indonesia.

### C) Doubles and the geometry of the layout

Doubles are traditionally played across the line of play, and the line is continued from the other side in the normal way. Here is an example with equal-end matching.

In some games the layout is allowed to extend from the ends of certain doubles as well as from the two sides, and this causes the layout to branch. A double where the layout can branch in this way is sometimes known as a 'spinner'.

We can classify connecting domino games according to the shape of the layout. Most traditional connecting games generally fall into categories depending on whether all, one or no doubles act as spinners. There are also a few where arms can be built in only one or more than four directions from the first tile, and a few where each player has their own separate layout. Some recently invented games make use of novel layout types and some extra categories have been added to cover these. In the diagrams below the blue tile represents the first tile played in the game and the arrows represent directions in which the layout can be extended from its open ends.

1. Single arm games.
These are games where the layout is built in just one direction from the initial play. Doubles are not spinners, and at any point in the game the layout hads just one open end where a tile can be added.
2. Line games.
This is the traditional and most usual form of connecting domino game. The layout is built from both ends of the initial tile (or from both sides in the common case where the layout is begun with a double played crosswise). Doubles are not spinners, though they are usually played across the line. The result is a layout with just two open ends.
3. Cross games
The first double played, and only the first double, is a spinner. The result is a layout with four arms forming a cross shape. For cross games started with a double there is quite often an additional rule that one tile must be played on each of the arms of the cross before any of them can be extended further. There are some 'double cross' games with the further rule that the second tile played on each arm must be a double. In a few games,
4. Star games.
There are some games that are started with a double from which more than four arms can grow. This can be the case in games of the trains family when each player has their own arm, or simply because the rules specify some larger number of arms. The result is a star-shaped layout.
5. Tree games.
All doubles are spinners. This produces a layout with many branches, since whenever a double is played on an arm, two extra open ends of the layout are created. For practical reasons the tiles built from the ends of the double are angled so that the arms of the tree are kept separate from each other and do not collide.
6. Network games.
Some recently invented domino connecting games allow tiles to be added in various orientations so that the layout can branch and rejoin and closed loops may be formed. The rules for where tiles can be placed and the resulting network shapes vary greatly from game to game.
7. Grid games.
Some recently invented domino connecting games require tiles to be positioned in a predefined two-dimensional grid. Many different types of grid and different connection rules are possible.
8. Games with disconnected layouts.
In some games the layout consists of several separate components - rows, columns or other tile groupings. In some cases each player has their own component or components and in others a player can play on any component. Again many different types of connection rules are possible.
9. Stack games.
Some games have been devised that exploit the fact that tiles can not only be laid out to form a two-dimensional layout but also stacked on top of one another, with various rules about what can be stacked and with various game objectives. In this group it is convenient also to include tile-matching games in which the tiles begin stacked and the play consists of removing accessible tiles.

### D) Game objectives and scoring

The traditional objective of domino connecting games is to be the first player to get all the tiles out of one's hand by playing them to the layout. This is known as "going out" or by some authors as "going domino". On pagat.com card games with this objective are called 'shedding games', so the same term is used here. There are some games where the main aim is to score points by achieving certain patterns on the layout, though there may also be points for going out. This enables domino connecting games to be grouped into the following categories according to the main objective:

Shed to layout.
The chief or only aim is to play all one's tiles and go out, or failing that to minimise the number of value of dominoes held when another player goes out or the game becomes blocked.
Bergen scoring.
Players score for placing equal numbers at the open ends of the layout.
Fives and threes family.
In these games it is the total of the numbers on all the open ends that is important. In Fives games, a player scores for making this total a multiple of 5. Less common are games where players score for making a multiple of 3. However, the game Fives and Threes, with scores for multiples of 5 and multiples of 3 is popular in some parts of England.
Other patterns
Recently invented games award scores for all kinds of patterns in the layout - playing a tile whose ends match more than one previous tile simultaneously, creating a repeating pattern, creating chains of continually increasing or decreasing numbers, creating an enclosed space in a network. The possibilities for new scoring systems are virtually limitless.