DATA MODELS. RECORD-BASED Models: OBJECT-BASED Models: HYBRID_BASED LOGICAL Models: PHYSICAL DATA Model. Here we have the following Models:

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Simon Baldwin
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1 DATA MODELS Here we have the following Models: Record-based Logical Models Object-based Logical Models Hybrid-based Logical Models Physical Data Models RECORD-BASED Models: Hierarchical Model - based on trees. Network Model - based on graphs Relational Model - based on tables and relationships, E-R model, semantic model. OBJECT-BASED Models: E-R model O-O model Binary model Semantic model Infological model Functional data model And others. HYBRID_BASED LOGICAL Models: A combination of the above PHYSICAL DATA Model Unifying Model Frame Memory, Etc.

2 NETWORK and HIERARCHICAL Data Base Management Systems For example: 1. branch, customer and account records 2. a pointer to the last record above 3. one status variable Commands: get locate a record in the DB and set the currency pointer to it. copy that record from the database to the appropriate area template this get must specify which tree in the forest DB. a) get first <record type> where <condition> b) get next <record type> where <condition> c) get next within parent where <condition> Examples: 1. Select CB. get first unique customer where customer.name = "CB"; print (customer.address); 2. Print an account belonging to CB with balance greater than $10,000 (if one exists) get first account where customer. name = "CB" and account.balance > $10000; if status = 0 then print (account.number); 3. Within a data base tree print the account number of all the accounts on the balance greater than $500. get first unique account where account. balance > $500; while status = 0 loop begin print (account.number); get next account where balance> $500 end. In system R2000: list customer. name, customer.city while customer has balance > $5000

3 4. Locate in a particular sub-tree (within parent). Print the total balance of all accounts belonging to CB. sum = 0; get first customer where customer. name = "CB"; get next within parent account; while status = 0 loop begin sum = sum + account.balance; get next within parent account; end; print(sum); Updating: Insert, Replace, Delete 5. To add new customer Bugs to Wonderland branch customer.name = "Bugs"; customer.street = "Tweety Road"; customer.city = "Disneyland"; insert customer where branch.name = "Wonderland"; (Note: it will not have an account number!) 6. To create a new account 655 for customer account. number: = 655; account. balance: = 100; insert account where customer. name = "Bugs ; 7. To change customer city of Bugs. get hold first customer where customer. name: = "Bugs customer. city: = "Warner Brothers"; replace; (Note: the hold that the system is aware that a modification will take place). 8. To delete account 655. (1 record) get hold first account where account. number = 655; delete; 9. To delete entire sub-tree rooted by that record. Delete customer CB and all his accounts. get hold first customer where customer. name = "CB"; delete;

4 The PARADIGM from CPS510 Let us go back and examine our example of S, P and SP. The data structure diagram (Bachman) of an n:m relationship between salespersons S and products P is represented as 1:n relationships between salespersons and products and a relationship SP. S P SP relationship Examples 1. For each salesperson, find the product numbers, he/she supplies. input the salesperson's identification to the field SNR in the salesperson's record. more-sp-records= "yes" find any S using SNR in S find first SP within S-SP loop until more-sp-records = "no" get SP keep the value of the field PNR in SP-record so that it can later be sent to the terminal-user find next SP within S-SP end loop free all send the retained PNR numbers to user terminal. Note: using uses the record type. get the record goes to user-area -> buffer can be referred to by field name within the record. free causes the current records of the program to be released so they can be used by other programs. i.e. read or updated. 2. Searching for records with a particular value in a given field read the salesperson's name into the field SNAME in S move-salesman = "yes" find any S using SNAME in S until move-salesman = "no" loop get S keep SNR and city to be displayed later find duplicate S using SNAME in S end loop. send the retained SNRs and cities to the terminal. The aim is to find all salespersons with a particular name. It is assumed in the program the SNAME is defined as a key field in the conceptual schema; but has to be non-unique key; duplicates not allowed is not an option that we can take in the definition of the key field.

5 Other DML Commands The find command locates a record and the get loads it into template. 1. Simple: customer.name: = "CB"; find any customer using name; get customer; print (customer.street); customer. city: = "Wonderland"; find any customer using city; while DB-status = 0 loop begin get customer print (customer.name); find duplicate customer using city; end. the duplicate locates records which reach the record-field. 2. To access records within a set. find first <record type> within <set-type> find next < record type> within <set-type> find owner within <set-type> 3. Creating new records/modify/delete. store <record type> modify <record type> erase [all] <record type> 4. Connect/Disconnect/Reconnect Connect a new record type into a particular set type (occurrence of set type) we must first store it and then connect <record type> to <set-type> account.number: = 601; account.balance = 0; store account; customer. name = "Brown"; find any customer using name; connect account to customer-account; Note: disconnect: removes a record type from the set-type. reconnect: moves a record of type <record type> from the set occurrence to another set occurrence of type set type: reconnect <record type> to <set type>.

6 Insertion/Retention/Deletion Insertion: manual (explicitly) by executing connect automatic (implicitly) by executing store. Retention: how and when a member record can be removed (there are restrictions). Deletion: when the record is the owner (refers to) Note: For the above we have: fixed, mandatory, and optional. Set Ordering: first: when insert - a record is inserted on top. last: when insert - a record is inserted on bottom. next: when insert - a record is inserted in next position from current position. prior: when insert - a record is inserted in prior position from current position sorted: kept sorted system default: kept by system.

7 Administration Facilities DBA Responsibilities Creating the DB Planning the logical DB and construction of the physical DB Maintenance of the data dictionary (description of fields, files, relationships, connections, etc) Controlling the use of data: The DBMS may collect statistics concerning the use of the DB, so that a check can be made (at intervals) to see whether the physical DB is organized in an optimized way from the point of view of the current uses for the data. Defining security and integrity constraints: Lists attempts of unauthorized use of data. Preparation of recovery procedures corresponding to various error situations that may arise Preparation of consistency control and periodical control of the consistency of the database Liaising with the users - advisory to users and programmers. Periodic checks for the reorganization of the DB Performance tuning Contact with software suppliers with a view to update the software, reporting errors, etc. Collection of information and material with a view of DB enhancement. Backing up the DB. Front End Subsystems and Tools A DBMS may be supplied with a variety of tools i.e. - word processors, spreadsheets, statistical packages, graphics, system shells, etc Tools that a DBMS may come with are totally open according to how sophisticated the package is in its environment. For example, upload and download tools (for micro and mainframe application development). Design and development of database tools. Menus and form driven interfaces may be used for data access. Natural language interfaces. Report writers which facilitate automatic report generation Business graphics. Application packages. CASE tools.

Chapter A: Network Model

Chapter A: Network Model Basic Concepts Data-Structure Diagrams The DBTG CODASYL Model DBTG Data-Retrieval Facility DBTG Update Facility DBTG Set-Processing Facility Mapping of Networks to Files A.1 Basic