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The ODM model assumes that a study's clinical data will consist of several kinds of entities. These include subjects, study events, item groups (e.g. forms, sections, item groupsdatasets), items, and annotations.

An item is an individual clinical data item, such as a single systolic blood pressure reading. Items are collected together into item groups.

An item group is is a closely related set of items that are generally analyzed together. ( Item groups are sometimes referred to as "records" and are associated with "panels" or "tables." .) Item groups are can be aggregated into formsother item groups of type form.

A form is An item group of type form is analogous to a page in a paper CRF book or electronic CRF screen. A form type item group generally collects a set of logically and temporally related information. A series of forms form type item groups is collected as part of a study event.

An item group of type dataset is analogous to a tabular dataset such as those used by statistical computing software to analyze data.

A study event is a reusable package of forms form type item groups, usually corresponding to a study data-collection event.

A study protocol design may include zero or more planned subject visits at which data will be collected. Each planned visit may correspond to one or more ODM study events and ODM study events may be used for more than one subject visit.

A subject is a patient is the entity participating in the study; for example, a patient in human clinical trials.

An annotation is is a comment applied to other entities; for example, to a subject, study event, form, item group, or item. Annotations can also be applied to pairs of entities.

The metadata of a study describes the types of study events, forms, item groups, and items, plus associated terminology that are allowed in the study. The metadata entities include StudyEventGroupDefs, StudyEventDefs, FormDefs, ItemGroupDefs, and ItemDefs.

A StudyEventGroupDef is a study building block that groups a number of smaller building blocks, which can themselves be StudyEventGroups or StudyEvents.

A StudyEventDef describes describes a particular type of study event (mostly by listing the types of forms item groups it can contain).A FormDef describes a particular type of form, in particular form type item groups).

An ItemGroupDef describes a particular type of item group that can include forms and datasets.

An ItemDef describes a particular type of item.

The clinical data of a study will typically have many actual study events corresponding to each StudyEventDef, many actual forms corresponding to each FormDefItemGroupDef of type form, and so on.

An ODM file (like any XML file ) consists of a tree of elementsof elements. The clinical data elements in an ODM file represent either the state of a clinical entity or a change to the state of that entity. These elements include the SubjectData, StudyEventData, FormData, ItemGroupData, ItemData, and Annotation elementsthe SubjectData, StudyEventData, ItemGroupData (nested when its corresponding ItemGroupDef is nested), ItemData, and Annotation elements.

Each such element contains key attributes that identify the data entity that it provides information for. Frequently, many data elements will correspond to a single data entity. This can occur when a series of updates are being applied to a single entity, or when an audit trail is being represented.Similarly, there are XML elements corresponding to metadata entities.

Note: Not Not all clinical studies organize their data into visits or forms. For such a study, it is appropriate to have a single common study event per subject, and/or a single common item group of type form per study event.