--- title: "PageSeeder primitives" source: https://dev.pageseeder.com/guide/document_modeling/pageseeder_primitives.html description: "PageSeeder primitives are fundamental building blocks including URIs (addressable entities), XLinks (associations between content and locations), Members (user accounts), Groups (social units), and Locators (anchor points). Each has system and public identifiers with specific attributes for managing documents, workflows, and permissions." last_updated: 2026-09-05T17:34:31+10:00 tokens: ~1563 --- # PageSeeder primitives This article introduces some of PageSeeder’s key primitives: - [URI](/reference/glossary/uri.md) - [XLink](/reference/glossary/xlink.md) - [Members](/reference/glossary/member.md) (and group membership) - [Groups](/reference/glossary/group.md) - Locators Understanding these primitives helps to explain the properties of higher level objects that are exposed through the API or the user interface. > **Note:** This is not an exhaustive list of primitives or their attributes—it is an introduction to those which are typically most significant. ## Identifiers for primitives Most primitives can be referenced by either a *system* identifier or a *public* identifier. | System Identifiers | Public Identifiers | | --- | --- | | **Assigned by PageSeeder** – for a single server only | **Assigned by a user** – can integrate externally managed IDs. For example, part numbers or ISBN codes | | **Immutable** – does not change over time | **Often mutable** – can be changed | | **Unique** – system-wide, within their class | **Unique** – within different sets | | **Examples** – URI ID, Member ID, XLink ID, Group ID | **Examples** – DocID, Group name | ## URI A URI is an addressable entity: it has a specific and unique URL. URIs can have *Locators*, which are anchor points to which XLinks can be attached*.* A URI can be shared between groups and it can resolve or map to the following: - A file or directory in the file system. - *OR* another addressable resource. - *OR* nothing! Every document in PageSeeder is a URI, including the following: - [PSML](/reference/glossary/psml.md) documents. - Non-native documents (*PDF*, Images, Videos, Office documents, text files, arbitrary XML). - Folders. URLs (aka External URIs) point to external resources. Special URI in group to attach general XLinks. [Labels](/psml/elements/element_labels.md) can be used to attach semantics. ### Attributes - `id` – a system and immutable identifier. - `docid` – a public identifier for the host *but* is mutable. - `scheme`, `host`, `port`, `path` – making the full URL unique. - `title` and `description` – similar to the role these play for Microsoft Word documents or PDF files.  - `mediatype` – the media type, for example, `application/vnd.pageseeder.psml+xml`  > **Note:** - GroupURIs (aka group folders) are used to share a URI. ## XLink XLinks are PageSeeder’s fundamental unit. They associate *content* created by a *Member* to *Locators* or to another *XLink.* An XLink can have custom semantics (through labels) and has built-in workflow attributes (status, due date and more). They can also be moderated and PageSeeder keeps track of moderation and modifications. An XLink can be assigned to a Member or shared between Groups through shared *URI*s. In PageSeeder, XLinks are used to represent the following: - Comments. - Task changes. - Document Versions. - Document Edits. - Cross references. - Links between documents. - … more. ### XLink sequences Attached to the same *Locator* or *XLink*, a sequence of XLinks can be used to represent: - A threaded discussion. - The changing states of a task. - The editing history of a document fragment. - A document workflow. By acting like a time machine on a *Locator, s*equences of XLinks provide the information that’s essential for formal audit trails.  ### Attributes - ID - Role & Title. - Content\* - Creation author & date. - Modification member & date. - Assign member & date. - Priority, status and due date. - Properties and labels. - Other XLinks in sequence. > **Note:** - The ID is a system and immutable identifier. - The author is generally a *Member* but not necessarily. - Properties and labels are used to provide semantics. - Priority, status, assigned member and due date are used for workflows. ## Locator A locator is an anchor point and is used to attach *XLink*s. It is addressable as `{uri(scheme, host, port, path)}#{fragment}`. For example, http://pageseeder.com/info.html#contact. A *URI* can have multiple locators: - Each locator is unique within the *URI*. There are special locators in PageSeeder: - For the document itself. - To refer to the group (for properties). The document default locator is used for: - Comments and tasks on the document. - Document version. The document fragment locators are used for: - Comments on document fragments. - Document editing. The group default locator is used for: - Group properties. ### Attributes - ID - Fragment > **Note:** - The Locator ID is an immutable system identifier. - The fragment is unique within a URI. ## Member A Member represents either a person who has an account on PageSeeder or another type of actor such as an external system. A Member is used to define credentials. XLinks in PageSeeder are generally authored by a member. ### Attributes - ID - Email - Username - Other/given name and family name. - Password - Notification preferences. > **Note:** - The Member ID is an immutable system identifier. - Both the email and username can be used as public identifiers *but* they are mutable. ## Group A Group is the social unit in PageSeeder and is essentially a collection of *Members* with specific *Membership* properties. Groups are configurable—the behavior and functionality is customizable at the group level. Groups can be *public* or *private*. There are special types of groups: - Personal groups. - Projects and sub-projects. ### Attributes - ID - Name - Description & related URL. - Visibility, owner and flags. - Template - Membership fields. > **Note:** - The Group ID is an immutable system identifier. - The name is a public identifier. ## Membership A *membership* expresses the relationship between a *Group* and a *Member*. It is used to define: - The role of the member in the group. - The notifications settings of the member for the group. - Group specific fields. ### Attributes - ID - Role - Notification & Email settings. - Moderator details. > **Note:** - The ID is an immutable system identifier. ## *Next...* See how PageSeeder primitive are specialized into [PageSeeder objects](/guide/document_modeling/pageseeder_objects.md).