🗊 Презентация Network Data Model

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Lecture 4. Network Data Model National Aviation University Computer Science Faculty Department of Software Engineering
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Lecture 4. Network Data Model National Aviation University Computer Science Faculty Department of Software Engineering

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CONTENTS Brief history Network data structure Network data structure operations Integrity constraints Advantages and drawbacks
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CONTENTS Brief history Network data structure Network data structure operations Integrity constraints Advantages and drawbacks

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Brief history
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Brief history

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Fields and record types Graphic notation:
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Fields and record types Graphic notation:

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Keys
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Keys

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Set type and instance (occurrence) Set owner. There is only one set owner record Set members. There may be 0, 1 or more set member records.
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Set type and instance (occurrence) Set owner. There is only one set owner record Set members. There may be 0, 1 or more set member records.

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Example of the set type and instance
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Example of the set type and instance

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Multilevel Hierarchy
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Multilevel Hierarchy

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Representation of m:n relationships
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Representation of m:n relationships

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Schema and instance of m:n relationships
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Schema and instance of m:n relationships

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Cycles and loops
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Cycles and loops

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Possible categories of network schemas
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Possible categories of network schemas

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Application and DBMS User Work Area (UWA) contains: current state indicators, records, error status.
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Application and DBMS User Work Area (UWA) contains: current state indicators, records, error status.

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Network data model operations Data selection (Query Language - QL): FIND - locates a described record occurrence GET - reads a record occurrence from...
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Network data model operations Data selection (Query Language - QL): FIND - locates a described record occurrence GET - reads a record occurrence from the database Data manipulation (Data Manipulation Language-DML): STORE - puts a record occurrence into the database INSERT - inserts member record into a set occurrence REMOVE - removes member record from a set occurrence DELETE - deletes current record from DB MODIFY - updates current record

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Data searching and selection
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Data searching and selection

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Fine the record by DB-key
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Fine the record by DB-key

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Fine the record by field values
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Fine the record by field values

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Scanning a Set Occurrence
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Scanning a Set Occurrence

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The next member record in the set occurrence
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The next member record in the set occurrence

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The prior member record in the set occurrence
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The prior member record in the set occurrence

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The first and the last member record in the set occurrence
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The first and the last member record in the set occurrence

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Location of the owner record of the current set occurence
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Location of the owner record of the current set occurence

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Example
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Example

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Put a record occurrence into the database create a record occurrence in UWA; execute the command STORE.
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Put a record occurrence into the database create a record occurrence in UWA; execute the command STORE.

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Attaching record occurrence from DB to the set occurrence Make required set occurrence the current of set type Make inserted record occurrence the...
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Attaching record occurrence from DB to the set occurrence Make required set occurrence the current of set type Make inserted record occurrence the current one Execute the command INSERT

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Remove a record occurrence of a certain type from a certain set occurrence Make designated record be the current one Execute the command REMOVE
Описание слайда:
Remove a record occurrence of a certain type from a certain set occurrence Make designated record be the current one Execute the command REMOVE

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Updating record occurrence The MODIFY command copies values from a record in UWA into the current record occurrence of the DB.
Описание слайда:
Updating record occurrence The MODIFY command copies values from a record in UWA into the current record occurrence of the DB.

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Deleting record occurrence from DB The DELETE command removes from DB the current record occurrence The set owner may be deleted when this set do not...
Описание слайда:
Deleting record occurrence from DB The DELETE command removes from DB the current record occurrence The set owner may be deleted when this set do not contains member records

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Advantages and drawbacks The network data model basically has the same advantages and drawbacks as hierarchical data model. The only basic difference...
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Advantages and drawbacks The network data model basically has the same advantages and drawbacks as hierarchical data model. The only basic difference of the network data model in comparison with hierarchical data model is the opportunity to represent many-to-many relationships.

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