What is the difference between persistent and transient objects?

-

Object

An object is a real-world entity with certain attributes that makes up the object's structure. Also, an object encapsulates the data code into a single unit which in turn provides data abstraction by hiding the implementation details from the user. Any object has two properties i.e. state & behavior hence, it's similar to the program variable but the object has a complex structure. There are two types of objects:

  • Transient object
  • Persistent object

Transient object

  • These objects exist during the execution but destroy once the program terminates.
  •  Transient Objects that have been just instantiated. Transient objects don't have representation and identifier values in the databases. The transient objects will be destroyed by the garbage collector if they don't have any use and reference in the database.
  • In this state, the database has the saved objects
  • Example- An entity from a repository comes under persistent objects


Persistent object

  • These objects persist & store in the database even if the program terminates. Whenever any object is created DBMS assigns a unique identifier called object identity & it's abbreviated as OID.
  •  Persistent Objects have representation in databases and identifiers. These objects are saved in the databases. Persistent objects are synchronized with that of the database.

  • The persistence in Object Oriented Databases is handled by creating Persistent Objects and Transient Objects. As stated above the persistent objects have representations in the databases. 

  • The objects are not kept in the database in this state of Hibernation
  • Until persisted, the creation of a new entity is called transients 



Comments

Post a Comment

Popular posts from this blog

Suppose that a data warehouse consists of the three dimensions time, doctor, and patient, and the two measures count and charge, where a charge is the fee that a doctor charges a patient for a visit. a) Draw a schema diagram for the above data warehouse using one of the schemas. [star, snowflake, fact constellation] b) Starting with the base cuboid [day, doctor, patient], what specific OLAP operations should be performed in order to list the total fee collected by each doctor in 2004? c) To obtain the same list, write an SQL query assuming the data are stored in a relational database with the schema fee (day, month, year, doctor, hospital, patient, count, charge)

-
Image
Solution: a) Star Schema is shown in the figure below: b) First, we should use the roll-up operation to get the year 2004(rolling-up from the day then month to a year). After getting that, we need to use the slice operation to select (2004). Second, we should use roll-up operation again to get all patients. Then, we need to use the slice operation to select (all). Finally, we get a list of the total fee collected by each doctor in 2004. So, 1. roll up from day to month to year 2. slice for year = “2004” 3. roll up on patient from the individual patient to all 4. slice for patient = “all” 5. get the list of the total fees collected by each doctor in 2004 c) Select doctor, Sum(charge) From fee Where year = 2004 Group by doctor
Read more

Suppose that a data warehouse consists of the four dimensions; date, spectator, location, and game, and the two measures, count and charge, where charge is the fee that a spectator pays when watching a game on a given date. Spectators may be students, adults, or seniors, with each category having its own charge rate. a) Draw a star schema diagram for the data b) Starting with the base cuboid [date; spectator; location; game], what specific OLAP operations should perform in order to list the total charge paid by student spectators at GM Place in 2004?

-
Image
  b) The specific OLAP operations to be performed are: 1. Roll-up on date from date id to year. 2. Roll-up on spectator from spectator id to status. 3. Roll-up on location from location id to location name. 4. Roll-up on the game from game id to all. 5. Dice with status= “students”, location name= “GM Place”, and year=2004
Read more

Suppose that a data warehouse for Big-University consists of the following four dimensions: student, course, semester, and instructor, and two measures count and avg_grade. When at the lowest conceptual level (e.g., for a given student, course, semester, and instructor combination), the avg_grade measure stores the actual course grade of the student. At higher conceptual levels, avg_grade stores the average grade for the given combination. a) Draw a snowflake schema diagram for the data warehouse. b) Starting with the base cuboid [student, course, semester, instructor], what specific OLAP operations (e.g., roll-up from semester to year) should one perform in order to list the average grade of CS courses for each BigUniversity student. c) If each dimension has five levels (including all), such as “student < major < status < university < all”, how many cuboids will this cube contain (including the base and apex cuboids)?

-
Image
a) A Snowflake Shema is shown in figure below: b) The specific OLAP operations to be performed: 1. Roll-up on course from course_id to department. 2. Roll-up on a student from student_id to university. 3. Dice on course, student with department ="CS" and university = "biguniversity" 4. Drill-down on a student from the university to student_name. c) N = 4 dimensions The cube will contain 54 = 625 cuboids.
Read more