Uniform Comparison of Data Models Using Containment Modeling - E. James WhiteHead

Introduction Containers fill many roles Containers fill many roles grouping and organizing data itemsgrouping and organizing data items model compound documentsmodel compound documents The data models of hypertext systems can be viewed as networks of containment relationships. Composites, links, anchors, objects …all are containers It is valuable to have a model focused on just the containment relationships among hypertext system entities.

Containment Data Models Paper describes about containment relationships, containment data models and application of this model. Paper describes about containment relationships, containment data models and application of this model. Subset of Entity relationship model. Subset of Entity relationship model. Entities signify hypertext abstractions such as works(doucments), links, anchors & container types. Entities signify hypertext abstractions such as works(doucments), links, anchors & container types. relationships are either a type of containment, storage or inheritance. relationships are either a type of containment, storage or inheritance. Key quality of containment data model is their ability to model systems uniformly, allowing a broad range of systems to be compared consistently. Key quality of containment data model is their ability to model systems uniformly, allowing a broad range of systems to be compared consistently.

Goals of Modeling Mechanism Goals of Modeling Mechanism Uniformity Uniformity Use a minimal set of system neutral abstractionsUse a minimal set of system neutral abstractions Utility Utility Answer basic questions about data modelAnswer basic questions about data model Are links to whole works, or to a subregion within a workAre links to whole works, or to a subregion within a work Are links separate from, or part of a work.Are links separate from, or part of a work. Support Analysis Support Analysis Tease out different design choicesTease out different design choices Graph Formalism Graph Formalism Communicate models quickly and intuitively with figures.Communicate models quickly and intuitively with figures. Concise Format Concise Format Fit many models on a single page, for easy comparisonFit many models on a single page, for easy comparison Cross Discipline Cross Discipline Capable of modeling other Content Management Systems.Capable of modeling other Content Management Systems.

Uniform way of Modeling Systems Uniform way of Modeling Systems Modeling Mechanism contain system neutral basic modeling blocks. For ex: links in Dexter hypertext model. Modeling Mechanism contain system neutral basic modeling blocks. For ex: links in Dexter hypertext model. Creating Data Models using Non-hypertextual entities mapped onto hypertext system abstractions. Modeling used: Extended Entity Relationship Model(ER model). Creating Data Models using Non-hypertextual entities mapped onto hypertext system abstractions. Modeling used: Extended Entity Relationship Model(ER model). Why ER ? Why ER ? Emphasis on static relationships.Emphasis on static relationships. Does not involve modeling behavioral aspects of system entitiesDoes not involve modeling behavioral aspects of system entities Elements of ER data model are entities and relationships. Elements of ER data model are entities and relationships. In modeling Hypertext systems In modeling Hypertext systems Entities represent hypertext abstractions such as works, anchors and links.Entities represent hypertext abstractions such as works, anchors and links. Relationships are of type Containment, inheritance and storageRelationships are of type Containment, inheritance and storage

Basic Static Containment Aspects of Containment Model Aspects of Containment Model Abstract Properties of Container Abstract Properties of Container Mathematic set of properties independent of a specific computer representationMathematic set of properties independent of a specific computer representation Containment: object belongs to one set(single) or many(multiple).Containment: object belongs to one set(single) or many(multiple). Membership: each object can belong to a set once(single), or many (multiple) times.Membership: each object can belong to a set once(single), or many (multiple) times. Ordering: persistently ordered, unordered, indexed, grouped.Ordering: persistently ordered, unordered, indexed, grouped. Containment typeContainment type Two ways to represent that a container contains a particular entityTwo ways to represent that a container contains a particular entity Referential – a pointer to another objectReferential – a pointer to another object Inclusion – contained object is a sub-part of container object.Inclusion – contained object is a sub-part of container object.

Containment Types Inclusion: item is physically part of container Referential containment types: Describes identifier storage On container On object On container and object First-class containment relationship A new container is introduced, and storage is delegated to it. Hybrid First-class container plus one other

Advanced Containments Containment Constraints Containment Constraints Type of contained objectsType of contained objects Number of contained objectsNumber of contained objects Typing of ContainerTyping of Container Dynamic Containment Dynamic Containment Mapping from objects to collections is generated by functionsMapping from objects to collections is generated by functions Queries can be used to determine collection membership Query results specify the endpoint of a single containment relationship Often used in hypertext versioning, where the query specifies a revision selection criteria within a versioned object Query typically returns a single object Storage of query predicate varies Query results specify the membership of the collection Query returns multiple objects

Hypertext System Data Models Modeling a broad set of systems Modeling a broad set of systems Monolithic Hypertext SystemsMonolithic Hypertext Systems NoteCards, KMS, Intermedia, HyperCard, Storyspace 1NoteCards, KMS, Intermedia, HyperCard, Storyspace 1 Dexter reference modelDexter reference model WWWWWW Link ServerLink Server Sun’s Link service, Microcosm, Chimera, MulticardSun’s Link service, Microcosm, Chimera, Multicard Open HyperbaseOpen Hyperbase Sepia, Hyperdisco and HURLSepia, Hyperdisco and HURL

Observations on Monolithic Hypertext systems Each System is modeled directly w/o any additional mapping beyond system abstractions to entities. Each System is modeled directly w/o any additional mapping beyond system abstractions to entities. KMS and HyperCard Systems KMS and HyperCard Systems links embedded within frame/card.links embedded within frame/card. do not have distinct identifiers & are not separable from frames/card.do not have distinct identifiers & are not separable from frames/card. links are modeled as separate entities.links are modeled as separate entities.

Observations on Monolithic Hypertext systems Story Space 1 and Notecards Model Story Space 1 and Notecards Model shows how the containment model shows similarities b/w system data model.shows how the containment model shows similarities b/w system data model. since both models have a single file that contains nodes and links.since both models have a single file that contains nodes and links. story space can be viewed as refinement of Notecard Model, adding notion of guard fields and anchor to its links.story space can be viewed as refinement of Notecard Model, adding notion of guard fields and anchor to its links.

Observations on Dexter model Concisely represents Dexter data model. Concisely represents Dexter data model. Collects huge amounts of data in single place Collects huge amounts of data in single place Easy to understand Easy to understand Good uniformity of modeling mechanism. Good uniformity of modeling mechanism.

The Web

Conclusion Containment data modeling is capable of uniformly and concisely modeling a wide range of existing data models Permits structural cross-comparison of system data models Dexter and the Web can be modeled, just like other hypertext systems Focuses on Modeling the static aspects of system data model. Could be used in modeling systems in other domains.