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Since URLs as location tend to change over time for whatever reason they are obviously inappropriate as stable references, but they are ubiquitously given as locations of digital objects. The analogy in the library world is the shelfmark and the insight that the mark in the bookshelf is not the correct way to point to the book, because the place of the book in the shelf tends to change over time for whatever reason.

In order to become a real pointer to the location of the digital object a resolution infrastructure for PIDs is necessary.

The analogy here is the order of the books depending on the alphanumerical order of the shelfmarks. Resolution systems enable client software to go from an identifier to current state information about the identified object, such as where and how to access the object. Such identifiers can persist over changes to the identified object, like changes in its location s , ownership, and other attributes — persistence that is vital for maintaining data integrity over time.

Investigations about references to digital objects in the web say that 7 from 10 such references in a scientific context are not accessible anymore for whatever reason reference rot, see hdl This means a significant loss of reproducibility of scientific results for instance, and this is expected to become even worse, because the portion of web references will increase especially due to references to data sources in scientific publications. Persistent identifiers can help to avoid this, because they can be adjusted in the case of changes, and they can make planned changes and obligations like citations transparent.

This is necessary but not sufficient for proper resolution. The responsibility for the content of the URL field in the handle however is in the hands of the owner of the PID, which is in most cases the owner of the prefix. PIDs can prevent link rots, because they distinguish the identity of an object from its location on the web. But this only works, if the field pointing to the location on the web is accurately maintained with respect to changes. Since a necessary location change in a PID is often caused by a more general decision like the change of technology in a repository or the change of the name of an institution, new locations often are needed for a huge amount of PIDs at the same time, such that automated processes are in general used for such changements.

In practice it is therefore often of advantage, that the owner of the PID has also control of the location of the particular object and even more that the owner of the prefix has also control of the location of all the objects, the PIDs under this prefix are pointing to. This means in general that PIDs should belong to trustful data repositories and not to individuals. Its focus is the registration of data in an early state of the scientific process, where lots of data is generated and has to become referable to collaborate with other scientific groups or communities, but where it is still unclear, which small part of the data will be cited or should be available for a long time period.

Another identifier system, which is widely used by the publishing industry for the persistent identification of journal articles and for tracking cross-linking through citations, is the Digital Object Identifier DOI. If a later registration of a digital object with a DOI is wanted for some reason, in most cases, depending on the characters used in the suffix, the PIDs can easily be transferred because the identifier systems use the same underlying Handle software and similar database schemata.

The Handle System is a general-purpose identifier resolution system that has been in place for many years. The prefix is used by client software to find the specific servers within the widely distributed resolution system that will be able to resolve the identifier. Existing identifiers can be easily structured as Handles in order to take advantage of the resolution system.


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For the resolution of a Handle like This allows to identify substructures of a web resource such as a number of frames in a video. If one wants to access such services also via the handle resolution, it is necessary to identify the fragment strings in the resolution process and hand them over to the resolved web resource. Technically this is done by a rather generic pattern matching process in the resolution of the PID that can be defined on a prefix level.

However Fragment or Template Support requires local resolution operations on web resource and cannot be mixed with generally resolvable references and citations. If this is required by science, one should create more granular digital objects. Data Types are additional metadata, closely coupled and stored in the PID database.

PID Information Types are special data types intended to be accessible before data processing and access They are mainly used for state information what is the data?

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The assignment of ePIC is to set up and maintain a highly reliable joint service with transparent policies for registering, storing and resolving persistent identifiers based on Handles for the research community. Please ask at support pidconsortium. This will also ensure that the overhead of the ePIC consortium will be small and restricted to essential services. It furthermore maintains the documentation of the ePIC software stack and an internal wiki for adminstration purposes. The chair of the the management is elected always for a one year period. This consortium will moderately grow in future.

Persistent data structures - GeeksforGeeks

The Multi Primary Administrators MPAs are members of DONA, that are responsible for a certain prefix namespace, which is determined by the numbers leading the first delimiter dot from the left. In higher level programming, machine data types are often hidden or abstracted as an implementation detail that would render code less portable if exposed. For instance, a generic numeric type might be supplied instead of integers of some specific bit-width. The Boolean type represents the values true and false. Although only two values are possible, they are rarely implemented as a single binary digit for efficiency reasons.

Many programming languages do not have an explicit Boolean type, instead interpreting for instance 0 as false and other values as true. Boolean data refers to the logical structure of how the language is interpreted to the machine language.

Computing & Information Systems

In this case a Boolean 0 refers to the logic False. True is always a non zero, especially a one which is known as Boolean 1.

Lesson 7.1: Introduction to data types

Composite types are derived from more than one primitive type. This can be done in a number of ways. The ways they are combined are called data structures. Composing a primitive type into a compound type generally results in a new type, e. Many others are possible, but they tend to be further variations and compounds of the above. For example a linked list can store the same data as an array, but provides sequential access rather than random and is built up of records in dynamic memory ; though arguably a data structure rather than a type per se , it is also common and distinct enough that including it in a discussion of composite types can be justified.

The enumerated type has distinct values, which can be compared and assigned, but which do not necessarily have any particular concrete representation in the computer's memory; compilers and interpreters can represent them arbitrarily. If a variable V is declared having suit as its data type, one can assign any of those four values to it. Some implementations allow programmers to assign integer values to the enumeration values, or even treat them as type-equivalent to integers. Since most character sets include the digits , it is possible to have a numeric string, such as "". However, many languages treat these as belonging to a different type to the numeric value Character and string types can have different subtypes according to the required character "width".

The original 7-bit wide ASCII was found to be limited, and superseded by 8 and bit sets, which can encode a wide variety of non-Latin alphabets Hebrew , Chinese and other symbols. Strings may be either stretch-to-fit or of fixed size, even in the same programming language. They may also be subtyped by their maximum size. Note: strings are not a primitive in all languages, for instance in C , they are composed from an array of characters. Types can be based on, or derived from, the basic types explained above.

Workshop on Persistent Objects (POS)

In some languages, such as C, functions have a type derived from the type of their return value. The main non-composite, derived type is the pointer , a data type whose value refers directly to or "points to" another value stored elsewhere in the computer memory using its address. It is a primitive kind of reference. In everyday terms, a page number in a book could be considered a piece of data that refers to another one.

Related terms:

Pointers are often stored in a format similar to an integer; however, attempting to dereference or "look up" a pointer whose value was never a valid memory address would cause a program to crash. To ameliorate this potential problem, pointers are considered a separate type to the type of data they point to, even if the underlying representation is the same. Any type that does not specify an implementation is an abstract data type. For instance, a stack which is an abstract type can be implemented as an array a contiguous block of memory containing multiple values , or as a linked list a set of non-contiguous memory blocks linked by pointers.

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