RELATIONAL MODEL OF DATABASES AND OTHER CONCEPTS OF DATABASES
- 1. RELATIONAL MODEL OF DATABASES AND OTHER CONCEPTS OF DATABASES BY EDWIN JACOB, PRANAV AND KARTHIK SUNDARMANI
- 2. Database Model • A Database model defines the logical design and structure of a database and defines how data will be stored, accessed and updated in a database management system. The various types of database models are • Hierarchical Model • Network Model • Relational Model
- 3. Relational Model in DBMS • Relational Model was proposed by E.F. Codd to model data in the form of relations or tables. • The model is comprised of rows and columns that use SQL as a query language for maintaining and querying the databases. • The basic structure of data in relational model is tables. • Tables are also known as relations in relational model. • Some popular relational data base management systems software's are • DB2 And Informix Dyanamic Server- IBM • Oracle And RDB – Oracle • SQL Server And Access - Microsoft
- 4. Benefits and Challenges of the Relational Model • Databases that use the relational model have advantages over those that use other models. These include simplicity of organization, ease of creation, ease of data retrieval, built-in data integrity, flexibility of queries (including the fact that programmers can write queries that weren’t anticipated by the database designer), and less data redundancy (due to data normalization). • However, o system is perfect. The relational model falls short in scalability, difficulty of setup, and slower searches and queries when compared to other database models.
- 5. Why do we need a Relational Database Model? • Database Management System is software that permits the user to create, define, manage and control the functions of the database. • For better understanding, the Relational database model is used as an extension of the database lying under the relational values. The RDBMS is entirely based on the relational model broadly deployed in many applications. • It is a common choice for information storage in a database especially in maintaining financial records, logistics data, manufacturing products, personnel data, and so on. It replaced the legacy of hierarchical databases and network databases because of its simple implementation and administration features. • Initially, RDBMS faced many failures but after many advancements it became a popular hit and applied in many reliable applications.
- 6. IMPORTANT TERMINOLOGIES • Attribute: Each column in a table is called Attributes. Attributes are the properties that define a relation. • Tuple: Each row in the relation is known as tuple. • Degree: The number of attributes in the relation is known as degree of the relation. • Cardinality: The number of tuples in a relation is known as cardinality. • Tables: Tables are stored along with entities.
- 7. Example : Historical Bridge Work Relation • consider the relation which might record historical experience with different types of bridges accumulated by a particular agency. The actual instances or rows of data are hypothetical. The attributes of this relation are: • PROJECT NUMBER - a 6-digit code identifying the particular project. • TYPE OF BRIDGE - a text field describing the bridge type. (For retrieval purposes, a numerical code might also be used to describe bridge type to avoid any differences in terminology to describe similar bridges). • LOCATION - The location of the project. • CROSSING - What the bridge crosses over, eg. a river. • SITE CONDITIONS - A brief description of the site peculiarities.
- 8. • ERECTION TIME - Time required to erect a bridge, in months. • SPAN - Span of the bridge in feet. • DATE - Year of bridge completion. • ACTUAL-ESTIMATED COSTS - Difference of actual from estimated costs. • These attributes could be used to answer a variety of questions concerning construction experience useful during preliminary planning.
- 9. Cont…. • As an example, suppose that a bridge is to be built with a span of 250 feet, located in Pittsburgh PA, and crossing a river with limestone sub-strata. In initial or preliminary planning, a designer might query the database four separate times as follows: • SELECT from BRIDGEWORK where SPAN > 200 and SPAN < 300 and where CROSSING = "river" • SELECT from BRIDGEWORK where SPAN > 200 and SPAN < 300 and where SITE CONDITIONS = "Limestone" • SELECT from BRIDGEWORK where TYPE OF BRIDGE = "Steel Plate Girder" and LOCATION = "PA" • SELECT from BRIDGEWORK where SPAN < 300 and SPAN > 200 and ESTIMATED LESS ACTUAL COST < 100,000. • Each SELECT operation would yield the bridge examples in the database which corresponds to the desired selection criteria. In practice, an input/output interpreter program should be available to translate these inquiries to and from the DBM and an appropriate problem oriented language.
- 10. Cont…. • The four queries may represent subsequent thoughts of a designer faced with these problem conditions. He or she may first ask, "What experience have we had with bridges of this span over rivers?" "What experience have we had with bridges of this span with these site conditions? What is our experience with steel girder bridges in Pennsylvania? For bridges of this span, how many and which were erected without a sizable cost overrun? We could pose many more questions of this general type using only the small data table.
- 11. Other Conceptual Models of Databases • While the relational model offers a considerable amount of flexibility and preserves considerable efficiency, there are several alternative models for organizing databases, • Hierarchical model • Network model • AI based model
- 12. Hierarchical Database Model • The hierarchical model is a tree structure in which information is organized as branches and nodes from a particular base. • As an example Given below, hierarchical structure for rented equipment costs. In this case, each piece of equipment belongs to a particular supplier and has a cost which might vary by the duration of use. To find the cost of a particular piece of equipment from a particular supplier, a query would first find the supplier, then the piece of equipment and then the relevant price.
- 13. Example 1 • The hierarchical model has the characteristic that each item has a single predecessor and a variable number of subordinate data items. • This structure is natural for many applications, such as the equipment cost information described above. However, it might be necessary to construct similar hierarchies for each project to record the equipment used or for each piece of equipment to record possible suppliers. • Otherwise, generating these lists of assignments from the database illustrated in the Figure would be difficult. • For example, finding the least expensive supplier of a crane might involve searching every supplier and every equipment node in the database to find all crane prices.
- 14. Example 2 • Let us assume that we have a main directory which contains other subdirectories. Each subdirectory contains more files and directories. Each directory or file can be in one directory only i.e. it has only one parent. • Here A is the main directory i.e. the root node. B1 and B2 are their child or subdirectories. B1 and B2 also have two children C1, C2 and C2, C3 respectively. They may be directories or other files. This depicts one- to- many relationships.
- 15. Advantages • Promotes data sharing. • It is conceptually simple due to the parent-child relationship. • Database security is enforced. • Efficient with 1: N relationships. • A clear chain of command or authority. • Increases specialization. • High performance. • Clear results.
- 16. Cont…. • A user can retrieve data very quickly due to the presence of explicit links between the table structures. • The referential integrity is built in and automatically enforced due to which a record in a child table must be linked to an existing record in a parent table, along with that if a record deleted in the parent table then that will cause all associated records in the child table to be deleted as well.
- 17. Disadvantages • When a user needs to store a record in a child table that is currently unrelated to any record in a parent table, it gets difficulty in recording and user must record an additional entry in the parent table. • This type of database cannot support complex relationships, and there is also a problem of redundancy, which can result in producing inaccurate information due to the inconsistent recording of data at various sites.
- 18. Cont…. • Change in structure leads to change in all application programs. • M: N relationship is not supported. • No data manipulation or data definition language. • Lack of standards. • Poor flexibility • Communication barriers • Organizational Disunity. • Rigid structure
- 19. Network Model • This model was formalized by the Database Task group in the 1960s. This model is the generalization of the hierarchical model. • This model can consist of multiple parent segments and these segments are grouped as levels but there exists a logical association between the segments belonging to any level. Mostly, there exists a many-to-many logical association between any of the two segments. • We called graphs the logical associations between the segments. Therefore, this model replaces the hierarchical tree with a graph-like structure, and with that, there can more general connections among different nodes. • It can have M: N relations i.e, many-to-many which allows a record to have more than one parent segment.
- 20. Cont… • Here, a relationship is called a set, and each set is made up of at least 2 types of record which are given below: i. An owner record that is the same as of parent in the hierarchical model. ii. A member record that is the same as of child in the hierarchical model.
- 21. Example 1 In the above figure, member TWO has only one owner ‘ONE’ whereas member FIVE has two owners i.e, TWO and THREE. Here, each link between the two record types represents 1 : M relationship between them. This model consists of both lateral and top-down connections between the nodes. Therefore, it allows 1: 1, 1 : M, M : N relationships among the given entities which helps in avoiding data redundancy problems as it supports multiple paths to the same record.
- 22. Example 2 • In this figure, we can see that the subject is the child class and student and degree are the parent classes. • So, the subject has two parent classes. STUDENT has one child and the Degree class also have one child. • This kind of relationship among entities represents the network model.
- 23. Advantages • It is fast data access with a network model. • The network model allows creating more complex and more strong queries as compared to the database with a hierarchical database model. A user can execute a variety of database queries when selecting the network model. • Sometimes, the network model is used to build computer network systems. • The network model is considered as an enhancement to the hierarchical database model.
- 24. Disadvantages • The network model is a very complex database model, so the user must be very familiar with the overall structure of the database. • Updating the database is a quite difficult and boring task. We need the help of the application programs that are being used to navigate the data.
- 25. Network model VS Hierarchical model VS Relational model: Network Data Model Hierarchical Data Model Relational Data Model Pointers or links are used to express the relationship between records. The relationship between records is of the parent-child type A relation(that contains a key for each record involved in the relationship) is used to represent the relationship between records. It is possible to implement the Many to many relationships. Many to many relationships cannot be expressed in Hierarchical Data Model It is easy to implement Many to many relationships. No problem of inconsistency exists in the Network model. The data inconsistency is possible when we update or delete some records. Its needs to maintain Data integrity and consistency by maintaining the database Normalization
- 26. Network Data Model Hierarchical Data Model Relational Data Model Record relationship implementation is quite complex due to the use of pointers. The method of implementing the record relationships is; · Simple · Natural · straightforward The use of a key or composite key field plays a role in making the process easy for the implementation of relationships. In-Network model record relations are physical. The record relations are physical in the Hierarchical data model. Data is organized logically in the form of rows and columns and stored in the table. The relational model does not maintain a physical connection among records. Searching for a record is easy since there are multiple access paths to a data element. Searching for a record is very difficult because we can retrieve a child only after going through its parent record. A unique, indexed key field is used to search for a data element in a relation. The network model is useful for representing such records that have many to many relationships. The hierarchical Data Model is useful only when there is some hierarchical character in the database. The relational model is useful for representing most of the real-world objects and relationships among the objects.
- 27. AI database model - frame data structure • Frame data structure used to represent a building design element. This frame describes the location, type, cost, material, scheduled work time, etc. for a particular concrete footing. • A frame is a general purpose data representation scheme in which information is arranged in slots within a named frame. • Slots may contain lists, values, text, procedural statements (such as calculation rules), pointers or other entities. Frames can be inter-connected so that information may be inherited between slots. The Figure illustrates a set of inter-connected frames used to describe a building design and construction plan. • Object oriented data representation is similar in that very flexible local arrangements of data are permitted. While these types of data storage organizations are active areas of research, commercial database systems based on these organizations are not yet available.
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