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===Hierarchies===

A special note about hierarchies - an asset may only ever be attached (related) to a hierarchy at **one point**. An asset can't be in two locations, two places in the org chart etc.

If you have a situation where you would like to place an asset in more than one hierarchy, consider using [[types|types]] instead, as these can fulfill a similar goal.

===Directional Names===

Relationships have directional names. As well as the main name that describes the relationship as a whole (ie. Water Supply or Mains Power), they also have a description that applies when the relationship is going upstream (from child to parent) and another description that applies when it is going downstream (from parent to child).

For example, the relationship 'Mains Power' is a physical relationship describing the power coming from the power grid.

It has a relationship name of 'Mains Power', but it's upstream name is 'Powered By' and it's downstream name is 'Powers'.

These directional names are used when trying to describe these relationships in plain language. Rather than saying 'The light bulb has a downstream Mains Power relationship with the switch', we instead say 'The light bulb is powered by the switch'. And vice-versa, 'The switch powers the light bulb'.

===Avoiding Cycles===

While ARDI can deal with cyclic relationships - a relationship that flows back up to its source - we generally suggest avoiding their use.

This is largely because ARDI is designed to have a clear concept of 'upstream' and 'downstream' relationships, and making a cycling relationship makes those terms difficult.

However, cyclic relationships to exist in real-world processes. //Closed-loop systems// and such as cooling and hydraulic systems and systems that maximise efficiency by re-circulating their water are common.

To get around this - while at the same time making the relationships between your assets even more informative - we suggest splitting loops such as this into **two** relationships.

In a hydraulic closed systems, you can have a 'Hydraulic Supply' and 'Hydraulic Return' relationship, which then clearly marks if the oil within the hydraulic line is travelling //to where it is used//, or //from where it has been used//.

===Similar Relationships===

In some applications your media remains the same as it passes through your process - for example, the water being pumped through your cooling system may change temperature, but it's always //water//.

However, in other applications, it's the processes job to **change** the media into different forms. 

A good example of this is in mining, where rock crushers usually send the crushed material to a //screen//, which separates it into small pieces and large pieces. The small pieces fall through the screen and continue the process while the large pieces are diverted back around to be crushed again.

At each stage, the media has a different name. For example, 'Coarse Ore' is fed into the crusher, but 'Granulated Ore' comes out through the screen on the other side. 

===Administering Relationships===

See the article [[Managing Relationships]] to see an example of how new relationships are created, existing relationships are edited, and useless ones removed.