Editing Transparency (human–computer interaction) (section)

== Types of transparency in distributed system ==

Transparency means that any form of [[distributed system]] should hide its distributed nature from its users, appearing and functioning as a normal centralized system.

There are many types of transparency:
* Access transparency – Regardless of how resource access and representation has to be performed on each individual computing entity, the users of a distributed system should always access resources in a single, uniform way. Example: SQL Queries
* [[Location transparency]] – Users of a distributed system should not have to be aware of where a resource is physically located. Example: Pages in the Web
* Migration transparency – Users should not be aware of whether a resource or computing entity possesses the ability to move to a different physical or logical location.
* Relocation transparency – Should a resource move while in use, this should not be noticeable to the end user.
* [[Replication (computer science)|Replication]] transparency – If a resource is replicated among several locations, it should appear to the user as a single resource.
* [[Concurrency (computer science)|Concurrent]] transparency – While multiple users may compete for and share a single resource, this should not be apparent to any of them.
* [[Failure transparency]] – Always try to hide any failure and recovery of computing entities and resources.
* [[Persistence (computer science)|Persistence]] transparency – Whether a resource lies in volatile or permanent memory should make no difference to the user.
* [[Capability-based security|Security transparency]] – Negotiation of cryptographically secure access of resources must require a minimum of user intervention, or users will circumvent the security in preference of productivity.{{cn|date=July 2020}}

Formal definitions of most of these concepts can be found in [[RM-ODP]], the Open Distributed Processing Reference Model (ISO 10746).

The degree to which these properties can or should be achieved may vary widely. Not every system can or should hide everything from its users. For instance, due to the existence of a fixed and finite [[speed of light]] there will always be more latency on accessing resources distant from the user. If one expects real-time interaction with the distributed system, this may be very noticeable.