Name resolution

In computer science, name resolution (also called name lookup) is the process of finding the entity that an identifier used in a certain context refers to.

Name resolution in computer languages

Expressions in computer languages can contain identifiers. The semantics of such expressions depend on the entities that the identifiers refer to. The algorithm that determines what an identifier in a given context refers to is part of the language definition.

The complexity of these algorithms is influenced by the sophistication of the language. For example, name resolution in assembly language usually involves only a single simple table lookup, while name resolution in C++ is extremely complicated as it involves:

• namespaces, which make it possible for an identifier to have different meanings depending on its associated namespace;
• scopes, which make it possible for an identifier to have different meanings at different scope levels, and which involves various scope overriding and hiding rules. At the most basic level name resolution usually attempts to find the binding in the smallest enclosing scope, so that for example local variables supersede global variables; this is called shadowing.
• visibility rules, which determine whether identifiers from specific namespaces or scopes are visible from the current context;
• overloading, which makes it possible for an identifier to have different meanings depending on how it is used, even in a single namespace or scope;
• accessibility, which determines whether identifiers from an otherwise visible scope are actually accessible and participate in the name resolution process.

Static versus dynamic

In programming languages, name resolution can be performed either at compile time or at runtime. The former is called static name resolution, the latter is called dynamic name resolution.

Examples of programming languages that use static name resolution include C, C++, Java, and Pascal. Examples of programming languages that use dynamic name resolution include Lisp, Perl, Python, Tcl, PHP, and REBOL.

Name resolution in computer networks

In computer networks, name resolution is used to find a lower level address (such as an IP address) that corresponds to a given higher level address (such as a hostname). Commands that allow name resolution are: nslookup and host. See Domain Name System, OSI Model.

Name resolution in semantics and text extraction

Also referred to as entity resolution, in this context name resolution refers to the ability of text mining software to determine which actual person, actor, or object a particular references refers to, by looking at natural language text.

Name resolution in simple text

For example, in the text mining field, software frequently needs to interpret the following text:

John gave Edward the book. He then stood up and called to John to come back into the room.

In these sentences, the software must determine whether the pronoun "he" refers to "John", or "Edward" from the first sentence. The software must also determine whether the "John" referred to in the second sentence is the same as the "John" in the first sentence, or a third person whose name also happens to be "John". Such examples apply to almost all languages, and not just English.

Name resolution across documents

Frequently, this type of name resolution is also used across documents, for example to determine whether the George Bush referenced in an old newspaper article as President of the United States is the same person as the George Bush mentioned in a separate news article years later about a man who is running for President. Because many people may have the same name, analysts and software must take into account substantially more information than just a name in order to determine whether two identical references ("George Bush") actually refer to the same specific entity or person.

Name/entity resolution in text extraction and semantics is a notoriously difficult problem, in part because in many cases there is not sufficient information to make an accurate determination. Numerous partial solutions exist that rely on specific contextual clues found in the data, but there is no currently known general solution.

For examples of software that might benefit from name resolution, see also:

• Attensity
• Aerotext
• Autonomy

See also

• namespace (programming)
• Scope (programming)
• Named entity recognition
• Naming collision